Project information:
Name: OpenTeacher
Homepage: OpenTeacher download | SourceForge.net
License: GPLv2
PLEASEEE!!! It’s not working on linux anymore… 
It has a problem with the wrong version of python, I think.
This software hasn’t had a new release in, like, 8 years now? So I suppose there is no one maintaining it anymore.
Also, its still requiring Python 2, which itself is not maintained as well anymore.
This would probably need a maintainer first updating the code, maybe even rewriting it. Not something Flathub can help you with unfortunately.
You could in theory write a manifest building the app and a Python 2 installation for personal use, but I highly doubt it would be permitted on Flathub.
IMO Flathub should also serve as a way to preserve legacy abandon software that is still useful to people, I’ve published such a an old app (one using Qt3, called PDFedit).
Just make sure sandbox perms are security sane and also tell in the description that the app is unmaintained so be careful to use it with untrusted data.