Just in case any Gimp users stumble on this:
The very popular gimp_gmic_qt plugin does not work with the snap (or flatpak) Gimp installations. These are sandboxed and do not include QT support required by the plug-in.
The snap version also affects other Gimp operations. Photography for example, Gimp will open a RAW image using Rawtherapee (or Darktable) as an intermediary application. Once preliminary processing is done, the image is sent back to Gimp. Obviously does not work with a sandboxed snap application.
What does work in the snap is Gimp python support. Plug-ins such as resynthesizer / heal-selection.py will work. (That comment about the python shebang #!/usr/bin/env python No problem so far with linux but for a Windows portable Gimp 2.10.18 user, it did need to be #!/usr/bin/env python2 )
No need for the snap version? Gimp 2.10.18 is packaged in the repo. Easy to install, regular installation. If QT5 is installed then the gimp_gmic_qt plugin will work. There is a version for focal on the gmic site.
No gimp-python plugin, all those python 2.7 plug-ins no longer work. There are python 2.7 packages in the repo but until a suitable gimp-python package is added Gimp is crippled for many users.
Final comment about the gimp-plugin-registry package: 160 scripts / 24 plug-ins Some of these have not worked since Gimp 2.6 About time it was dumped.
However, want to try in the Gimp 2.10 snap then unpack the deb and put the files in the snap Gimp user profile.