diff --git a/.github/workflows/example_tests.yml b/.github/workflows/example_tests.yml
index b722d3e..843268e 100644
--- a/.github/workflows/example_tests.yml
+++ b/.github/workflows/example_tests.yml
@@ -40,4 +40,4 @@ jobs:
         if: matrix.sumo_version == 'head'
         run: brew install --with-examples --HEAD sumo
 
-      - run: python $(brew --prefix sumo)/share/sumo/docs/examples/runAll.py
+      - run: python "$(brew --prefix sumo)/share/sumo/docs/examples/runAll.py"
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index 93540f5..eb8ae83 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -18,7 +18,7 @@ jobs:
         env:
           HOMEBREW_GITHUB_API_TOKEN: ${{ github.token }}
           PULL_REQUEST: ${{ github.event.pull_request.number }}
-        run: brew pr-pull --debug --tap=$GITHUB_REPOSITORY $PULL_REQUEST
+        run: brew pr-pull --debug --tap="$GITHUB_REPOSITORY" "$PULL_REQUEST"
 
       - name: Push commits
         uses: Homebrew/actions/git-try-push@master
@@ -30,4 +30,4 @@ jobs:
         if: github.event.pull_request.head.repo.fork == false
         env:
           BRANCH: ${{ github.event.pull_request.head.ref }}
-        run: git push --delete origin $BRANCH
+        run: git push --delete origin "$BRANCH"
diff --git a/Aliases/sumo@1.20 b/Aliases/sumo@1.21
similarity index 100%
rename from Aliases/sumo@1.20
rename to Aliases/sumo@1.21
diff --git a/Formula/sumo.rb b/Formula/sumo.rb
index d2669b8..be28333 100644
--- a/Formula/sumo.rb
+++ b/Formula/sumo.rb
@@ -1,18 +1,15 @@
 class Sumo < Formula
   desc "Simulation of Urban MObility"
   homepage "https://www.eclipse.dev/sumo"
-  url "https://sumo.dlr.de/releases/1.20.0/sumo-src-1.20.0.tar.gz"
-  sha256 "34320ba1695db74c769d6b4931cb6bc6ec5b26c37e556451ab29d3963d6af8ec"
+  url "https://sumo.dlr.de/releases/1.21.0/sumo-src-1.21.0.tar.gz"
+  sha256 "1a246c30159abd4b5a878c0ce4eba3779bc6fce95f9c815c5f45567ceaa4ea53"
   license "EPL-2.0"
   head "https://github.com/eclipse-sumo/sumo.git", branch: "main"
 
-  bottle do
-    root_url "https://github.com/DLR-TS/homebrew-sumo/releases/download/sumo-1.20.0"
-    sha256 cellar: :any, arm64_sonoma:  "de437553bbfff2c123b1e2c90f2bc0e35693cb34a1f371887891cd837577a279"
-    sha256 cellar: :any, arm64_ventura: "0416595756b2ce18e84c6c760257982210ffb3df07c9c43f60ade8a26d34578d"
-    sha256 cellar: :any, ventura:       "711ff64f1d59c52b669a340cc3924097cdc1bbbc0000042b28e13156051d5f21"
-    sha256 cellar: :any, monterey:      "dd3c1d156ed3a48fbe61227a314b213ae4c6c903cf03edb4f5e344b3689a09c3"
-  end
+  # stable do
+  #   url "https://sumo.dlr.de/releases/1.21.0/sumo-src-1.21.0.tar.gz"
+  #   sha256 "1a246c30159abd4b5a878c0ce4eba3779bc6fce95f9c815c5f45567ceaa4ea53"
+  # end
 
   option "with-examples", "Install docs/examples and docs/tutorial folder"
 
diff --git a/Formula/sumo@1.20.0.rb b/Formula/sumo@1.20.0.rb
new file mode 100644
index 0000000..40f7f14
--- /dev/null
+++ b/Formula/sumo@1.20.0.rb
@@ -0,0 +1,136 @@
+class SumoAT1200 < Formula
+  desc "Simulation of Urban MObility"
+  homepage "https://www.eclipse.dev/sumo"
+  url "https://sumo.dlr.de/releases/1.20.0/sumo-src-1.20.0.tar.gz"
+  sha256 "34320ba1695db74c769d6b4931cb6bc6ec5b26c37e556451ab29d3963d6af8ec"
+  license "EPL-2.0"
+  head "https://github.com/eclipse-sumo/sumo.git", branch: "main"
+
+  bottle do
+    root_url "https://github.com/DLR-TS/homebrew-sumo/releases/download/sumo-1.20.0"
+    sha256 cellar: :any, arm64_sonoma:  "de437553bbfff2c123b1e2c90f2bc0e35693cb34a1f371887891cd837577a279"
+    sha256 cellar: :any, arm64_ventura: "0416595756b2ce18e84c6c760257982210ffb3df07c9c43f60ade8a26d34578d"
+    sha256 cellar: :any, ventura:       "711ff64f1d59c52b669a340cc3924097cdc1bbbc0000042b28e13156051d5f21"
+    sha256 cellar: :any, monterey:      "dd3c1d156ed3a48fbe61227a314b213ae4c6c903cf03edb4f5e344b3689a09c3"
+  end
+
+  option "with-examples", "Install docs/examples and docs/tutorial folder"
+
+  depends_on "cmake" => :build
+  depends_on "fontconfig"
+  depends_on "fox"
+  # indirect dependencies due to fox
+  depends_on "freetype"
+  depends_on "gettext"
+  depends_on "jpeg-turbo"
+  depends_on "libice"
+  depends_on "libpng"
+  depends_on "libtiff"
+  depends_on "libx11"
+  depends_on "libxcursor"
+  depends_on "libxext"
+  depends_on "libxfixes"
+  depends_on "libxft"
+  depends_on "libxi"
+  depends_on "libxrandr"
+  depends_on "libxrender"
+  depends_on "mesa"
+  depends_on "mesa-glu"
+
+  depends_on "proj"
+  depends_on "python" if build.head? && build.with?("examples")
+  depends_on "xerces-c"
+
+  depends_on "ffmpeg" => :optional
+  depends_on "gdal" => :optional
+  depends_on "gl2ps" => :optional
+  depends_on "open-scene-graph" => :optional
+  depends_on "swig" => :optional
+
+  # workaround due to dependency gdal -> numpy -> openblas -> gcc (originally gfortran)
+  # (use 'brew deps --tree sumo' to see dependencies of higher levels)
+  # also see: https://github.com/davidchall/homebrew-hep/issues/28
+  cxxstdlib_check :skip
+
+  def install
+    # cf. https://rubydoc.brew.sh/Formula.html#std_cmake_args-instance_method
+    cmake_args = *std_cmake_args(find_framework: "LAST")
+
+    # bottling uses default formula options and we want minimal requirement bottles,
+    # therefore, by default, do not check for optional libs
+    if build.with?("ffmpeg") ||
+       build.with?("gdal") ||
+       build.with?("gl2ps") ||
+       build.with?("open-scene-graph")
+      ohai "Enabling check for optional libraries..."
+      cmake_args << "-DCHECK_OPTIONAL_LIBS=ON"
+    else
+      cmake_args << "-DCHECK_OPTIONAL_LIBS=OFF"
+    end
+
+    # If found, SWIG is enabled by default by sumo cmake config step
+    # but Java/Python library paths found by cmake might still be broken,
+    # so we disable SWIG by default here.
+    cmake_args << "-DSWIG_EXECUTABLE=\"\"" if build.without?("swig")
+    # XXX: pointers for getting '--with-swig' to work:
+    # cmake_args << "-DJAVA_HOME=#{Formula["openjdk"].opt_prefix}/libexec/openjdk.jdk/Contents/Home"
+    # cmake_args << "-DPython_ROOT_DIR=#{Formula["python"].opt_prefix}"
+
+    mkdir "build/cmake-build" do # creates and changes to dir in block
+      system "cmake", "../..", *cmake_args
+      system "make"
+      system "make", "install"
+      system "make", "examples" if build.head? && build.with?("examples")
+    end
+
+    if build.with?("examples")
+      (pkgshare/"docs").install "docs/examples"
+      (pkgshare/"docs").install "docs/tutorial"
+    end
+  end
+
+  def caveats
+    <<~EOS
+      In order to let X11 start automatically whenever a GUI-based SUMO application
+      (e.g., "sumo-gui") is called, you need to log out and in again.
+      Alternatively, start X11 manually by pressing cmd-space and entering "XQuartz".
+
+      Don't forget to set your SUMO_HOME environment variable:
+        export SUMO_HOME="#{prefix}/share/sumo"
+
+      Please report any problems with this formula directly to the eclipse-sumo/sumo issue tracker:
+      https://github.com/eclipse-sumo/sumo/issues
+
+    EOS
+  end
+
+  test do # will create, run in and delete a temporary directory
+    # This small test verifies the functionality of SUMO.
+    # Run with 'brew test sumo'.
+    # Options passed to 'brew install' such as '--HEAD' also need to be provided to 'brew test'.
+
+    (testpath/"nodes.xml").write <<~EOS
+      <nodes>
+        <node id="0" x="0.0" y="0.0"/>
+        <node id="1" x="500.0" y="0.0"/>
+      </nodes>
+    EOS
+
+    (testpath/"edges.xml").write <<~EOS
+      <edges>
+        <edge id="0to1" from="0" to="1" numLanes="2" speed="30"/>
+      </edges>
+    EOS
+
+    system "#{bin}/netconvert", "-n", "#{testpath}/nodes.xml", "-e", "#{testpath}/edges.xml", "-o",
+           "#{testpath}/net.xml"
+
+    (testpath/"flows.xml").write <<~EOS
+      <routes>
+        <flow id="0to1" from="0to1" to="0to1" end="3600" vehsPerHour="1000"/>
+      </routes>
+    EOS
+
+    system "#{bin}/sumo", "-n", "#{testpath}/net.xml", "-r", "#{testpath}/flows.xml"
+  end
+end
diff --git a/README.md b/README.md
index 187bc29..aa1a66d 100644
--- a/README.md
+++ b/README.md
@@ -26,12 +26,12 @@ If you want to use `sumo-gui` and/or `netedit`, you need to install XQuartz as a
 
 ## Usage
 
-By default, the above command lines install a bottled SUMO stable version (currently ```1.20.0```) with minimal requirements (```fox```, ```proj```, ```xerces-c```).
+By default, the above command lines install a bottled SUMO stable version (currently ```1.21.0```) with minimal requirements (```fox```, ```proj```, ```xerces-c```).
 Alternatively, ```brew``` can compile SUMO from source with the following command line options:
 
 
     brew install [OPTIONS] sumo
-    
+
     ==> Options
     --with-examples
         Install docs/examples and docs/tutorial folder
diff --git a/update_formula.sh b/update_formula.sh
old mode 100755
new mode 100644
index 7ed0429..8df4cba
--- a/update_formula.sh
+++ b/update_formula.sh
@@ -8,19 +8,19 @@ FORMULA_NAME=dlr-ts/sumo/sumo
 README_FILE=README.md
 
 # check for cmd line parameters
-if [ $# -ne 2 ]; then
-    echo ""
-    echo "Usage: $0 <NEW_VERSION> <SUMO_SRC_URL>"
-    echo "Examples:"
-    echo "    NEW_VERSION: 1.3.1"
-    echo "    SUMO_SRC_URL: https://github.com/eclipse-sumo/sumo/archive/v1_3_1.tar.gz"
-    echo ""
-    exit 1
+if [[ $# -ne 2 ]]
+then
+  echo ""
+  echo "Usage: $0 <NEW_VERSION> <SUMO_SRC_URL>"
+  echo "Examples:"
+  echo "    NEW_VERSION: 1.3.1"
+  echo "    SUMO_SRC_URL: https://github.com/eclipse-sumo/sumo/archive/v1_3_1.tar.gz"
+  echo ""
+  exit 1
 fi
 
-NEW_VERSION=$1
-SUMO_SRC_URL=$2
-DATE_STRING=$(date +"%Y-%m-%d")
+NEW_VERSION="$1"
+SUMO_SRC_URL="$2"
 NEW_MAJOR=$(echo "${NEW_VERSION}" | awk -F . '{ print $1 }')
 NEW_MINOR=$(echo "${NEW_VERSION}" | awk -F . '{ print $2 }')
 NEW_PATCH=$(echo "${NEW_VERSION}" | awk -F . '{ print $3 }')
@@ -31,50 +31,50 @@ brew uninstall sumo
 brew install sumo
 
 # figure out version number
-OLD_VERSION_WITH_REVISION=$(brew ls sumo --versions | awk '{print $2}')
+OLD_VERSION_WITH_REVISION=$(brew ls sumo --versions | awk '{print $2}' || true)
 OLD_VERSION=$(echo "${OLD_VERSION_WITH_REVISION}" | awk -F _ '{print $1}')
 OLD_MAJOR=$(echo "${OLD_VERSION}" | awk -F . '{ print $1 }')
 OLD_MINOR=$(echo "${OLD_VERSION}" | awk -F . '{ print $2 }')
 OLD_PATCH=$(echo "${OLD_VERSION}" | awk -F . '{ print $3 }')
-echo "old sumo version: '$OLD_VERSION'"
+echo "old sumo version: '${OLD_VERSION}'"
 
 # generate full string (including version number) for formula class name
-FORMULA_CLASS_NAME="SumoAT$(echo $OLD_VERSION | sed 's/\.//g')"
-echo "formula class name: '$FORMULA_CLASS_NAME'"
+FORMULA_CLASS_NAME="SumoAT${OLD_VERSION//./}"
+echo "formula class name: '${FORMULA_CLASS_NAME}'"
 
 ARCHIVED_FORMULA_FILENAME="sumo@${OLD_VERSION}.rb"
- 
+
 # archive old formula
 echo "copying formula to Formula/${ARCHIVED_FORMULA_FILENAME} and updating class name of archived formula..."
-sed "s/class Sumo/class ${FORMULA_CLASS_NAME}/" Formula/sumo.rb >> Formula/${ARCHIVED_FORMULA_FILENAME}
+sed "s/class Sumo/class ${FORMULA_CLASS_NAME}/" Formula/sumo.rb >>Formula/"${ARCHIVED_FORMULA_FILENAME}"
 echo "done archiving old formula!"
 
 echo "creating git branch"
 git checkout -b sumo
 
 echo "adding archived formula to git"
-git add Formula/${ARCHIVED_FORMULA_FILENAME}
+git add Formula/"${ARCHIVED_FORMULA_FILENAME}"
 git commit -m "sumo: archive formula for version ${OLD_VERSION}"
 
 ### BUMP formula version (https://docs.brew.sh/Manpage#bump-formula-pr-options-formula)
 echo "bumping formula version..."
-brew bump-formula-pr -v --write-only --no-audit --url=${SUMO_SRC_URL} ${FORMULA_NAME}
+brew bump-formula-pr -v --write-only --no-audit --url="${SUMO_SRC_URL}" "${FORMULA_NAME}"
 # remove bottle block
 # NOTE: dirty hack assumes lines 12-17 (including extra blank line)
-sed '12,17d' /usr/local/Homebrew/Library/Taps/dlr-ts/homebrew-sumo/Formula/sumo.rb > Formula/sumo.rb
+sed '12,17d' /usr/local/Homebrew/Library/Taps/dlr-ts/homebrew-sumo/Formula/sumo.rb >Formula/sumo.rb
 git add Formula/sumo.rb
 git commit -m "sumo: update formula to v${NEW_VERSION}"
 
 ### UPDATE alias link
 echo "updating Alias symlink..."
-git mv Aliases/sumo\@${OLD_MAJOR}.${OLD_MINOR}.${OLD_PATCH} Aliases/sumo\@${NEW_MAJOR}.${NEW_MINOR}.${NEW_PATCH}
+git mv Aliases/sumo@"${OLD_MAJOR}.${OLD_MINOR}.${OLD_PATCH}" Aliases/sumo@"${NEW_MAJOR}.${NEW_MINOR}.${NEW_PATCH}"
 git commit -m "sumo: update alias"
 
 ### UPDATE version number in README.md
 echo "updating version number in README.md"
-sed "s/${OLD_VERSION}/${NEW_VERSION}/" ${README_FILE} >> ${README_FILE}.NEW
-mv ${README_FILE}.NEW ${README_FILE}
-git add ${README_FILE}
+sed "s/${OLD_VERSION}/${NEW_VERSION}/" "${README_FILE}" >>"${README_FILE}.NEW"
+mv "${README_FILE}.NEW" "${README_FILE}"
+git add "${README_FILE}"
 git commit -m "update version number in README"
 
 echo "You now need to create a pull request from the new branch to trigger the workflows ..."