MathMap is compiling and running good on Ubuntu and I recently made an RPM for Fedora33. I didn't upload it because it has some strange dependencies but it does work.
If Gimp is started from a terminal the MathMap composer tab throws a non-fatal error message like this:
(mathmap:2424): Gdk-CRITICAL **: IA__gdk_cairo_create: assertion 'GDK_IS_DRAWABLE (drawable)' failed
If one of the stand alone filters is used no error message.
I suspect it could be caused by MathMap using GTK2 and not GTK3. I will probably be checking this out in the future. I've got a spare computer I can compile on and not worry about anything getting affected.
I also like the idea of a better MathMap appimage. Putting a Gimp filter into user space is realistic. Also Gimp filters only use the appimage as an installer.
Cheers for now.