> is it even possible to do read-write to a git repo over https instead of ssh?

Yes; it's not only possible but very common: https://docs.github.com/en/get-started/git-basics/about-remo...

(IIRC it is in fact actually even sometimes preferable from a security standpoint; or at least that's the tentative conclusion I've reached under a few specific circumstances over the years, although the exact details elude my memory at the moment.)

Git doesn’t even need to be “hosted” in the traditional sense. The whole point of it is that it is distributed and you don’t actually need a centralized source of truth.