To build and install the snap:
$ snapcraft
...
# For snapd version 2.14:
$ sudo snap install --devmode --force-dangerous plexmediaserver_*_amd64.snap
# For snapd version 2.15+:
$ sudo snap install --devmode --dangerous plexmediaserver_*_amd64.snap
You may reach the web interface at http://:32400/web/index.html