Well sourcehut can be self hosted as well (ain't it OS anyways?):

https://sr.ht/~sircmpwn/sourcehut https://man.sr.ht/installation.md

That said, sourcehut has privacy features, and libre oriented features gitlab doesn't. But I understand, as of now, without webUI, as it is, it's pretty hard to adopt sourcehut, and even when it finally does, having invested on gitlab (and even majority on github), which implies time and resources, might not be an easy thing to try sourcehut any ways.