I just run your script on a Debian 11. The appImage created in /opt/gimp once start, run the native GIMP .deb from the distribution, so 2.10.22 in my case. I removed the native GIMP, and retry. Then ...

get-pip.py install [options] [package-index-options] ... get-pip.py install [options] -r [package-index-options] ... get-pip.py install [options] [-e] ... get-pip.py ...