The NIK collection is very much a Windows installation, dozens of files, hundreds of registry entries. Do not expect it to work in linux even in WINE.
For shellout.py (or other python plugins) to work it does of course require a Gimp python2 installation. Not there in Mint 21. It can be 'added' with an appimage.
see:
https://www.gimp-forum.net/Thread-Python...3#pid29963#
https://github.com/TasMania17/Gimp-Appim...-for-Linux
https://i.imgur.com/fWY3ezt.mp4
For shellout.py (or other python plugins) to work it does of course require a Gimp python2 installation. Not there in Mint 21. It can be 'added' with an appimage.
see:
https://www.gimp-forum.net/Thread-Python...3#pid29963#
https://github.com/TasMania17/Gimp-Appim...-for-Linux
https://i.imgur.com/fWY3ezt.mp4