Anyone know if it is possible to fork a repository on some other git hosting service on github?
However you can mimic some of it manually by cloning and pushing. You’d also need to maintain the upstream relationship manually.
Most providers have a concept of imports that work much like a fork would. Gitlab specifically will import the repo, wiki, issues, and likely other bits. Everything is treated as a snapshot in time but since the repository and wiki are both git, you can merge upstream changes later. There's also the concept of mirroring that'll automatically push or pull changes from other providers.
I haven't done an import/fork to Github to know how that experience is but I've done a good few with Gitlab to know that it works rather well.