As DevOps engineer I've used and managed both Gitlab and Github extensively, and Gitlab is just so much better. Things make sense there. Shame that it's so darn expensive.
I can see how GitHubs self hosting story might be worse, because it’s just not designed for that, most companies don’t do it anymore, and I believe the product is deprecated.
As for doing devops from the platforms, I always found GitHub Actions better than GitLab CI, but I realise many feel the opposite.