See if the maintainer is willing to accept email patches. You can clone the repo from the github link, make changes, and generate a patch which you can send to a maintainer.

Unfortunately it's a bit tough to avoid github, it's like the facebook of programmers. I don't see any particular reason why it's bad though? If anything, it might improve with microsoft now owning it.

I can also merge from GitLab (or other server) forks too, I think? I've never tried doing that, but it sounds like something that should be trivial

Git is designed to be distributed, you could push to someone else’s repo and they can then push to GitHub for you.