Gitlab’s UI is extremely terrible. It’s hard to even explain how bad it is.

Once you get used to it, it's not so bad which is probably true for all functional UIs. I switch between gitlab and GitHub quite a lot and I can't say which one is objectively better. I do like that cross-linking is easier in GitHub but I prefer gitlab ci over GitHub actions. Too bad that gitlab ci runner has removed the command to run ci locally but third party foss solutions are there.