This particular flatpak is a bare bones gimp. It won't load G'mic, I assume it doesn't include a QT environment. It will load both my python and scheme scripts though, that's nice. I assume when they release a final stable version of Gimp 2.10, it will include those libraries. The Gimp 2.8.22 flatpak does and has no problem with G'mic.
For anyone running Linux, here is the install command:
flatpak install gimp-2.10.0-RC2-x86_64.flatpak
Here is the uninstall command:
flatpak uninstall org.gimp.GIMP/x86_64/dev