As far as I can see the gimp.org Gimp 3.0 appimage (all 450 MB of it) is based on Debian buster and a Gimp 3.0 gmic_gimp_qt needs to be compiled in that Debian with Gimp 3.0 libraries.
You could try this light-weight Gimp 3.0 version which is based on 'buntu
Will it get updated to Gimp 3.02 - maybe not - dependencies are getting to be a problem. It should work with Mint 21/22 (it works in my kubuntu 22.04 / 24.04) Remember you do need QT5 for the plugin.