Gitlab and github ci is fine until you're working in an environment with major compliance requirements for self hosted everything and/or basically infinite build history. At that point, sadly you're back in Jenkins world.

Another thing that kills Jenkins alternatives is just a sufficiently diverse number of languages/projects/build types. Plugin ecosystem sucks, but it's massive, and some of it will probably work for whatever use case. It's painful but your only alternative is also painful.. curating custom runner-containers for another ci tool with less existing historical effort to leverage