Panda Jim PPA is not an appimage, it is a regular repository install (provided the PPA is added to the sources list). If you have synaptic installed you can see it there.
The big diiference is ubuntu 20.04 comes with the gimp-python 2.7 package. Ubuntu 22.04/24.04 do not that package. Python 2.7 is deprecated replaced with python 3.x
The big diiference is ubuntu 20.04 comes with the gimp-python 2.7 package. Ubuntu 22.04/24.04 do not that package. Python 2.7 is deprecated replaced with python 3.x