Install Visual Studio 2022.
Download boost and put boost_1_81_0\boost into lib (so that you have lib\boost\<headers>).
If your Vic2 install location is different from
C:\Program Files (x86)\Steam\steamapps\common\Victoria 2
you must update VIC2_INSTALL_DIR in file_explorer\file_explorer.cpp (line 218) with the correct path.
Run build.bat, specifying Debug or Release, or leaving it blank for the default (Debug). Once the script finishes, run ..\open_v2_test_data\[Debug|Release]\file_explorer.exe, which will generate test_save_cmp.bin and test_scenario.bin before closing. Run it again to start Open V2.