Yeah, SLM can actually import games from Heroic! It scans your Heroic library (Epic, GOG, Amazon) and adds them as non-Steam shortcuts. Check the External Games feature (Ctrl+Shift+E).
And then you can also Use steamgrid.db to give them a custom Cover ;)
Good point about GitHub/Microsoft. Codeberg is on my radar but moving a whole repo with CI/CD, releases, issue templates etc is a bigger task. Maybe as a mirror first. For now GitHub is where the users are.
I like github! Have many repos there with SwitchBros Community, even if we often have DMCA repos 😕 because of Big N! I know that it is Microsoft but I also saw someone using Edge Browser on Linux, but who am I to Judge ;)? 🤷