I'm a strong advocate (after migration between various cloud CI providers free tiers when I worked in academia) of making your build process as agnostic as possible to the CI provider. That generally means putting things into shell scripts and calling them, which can be a bit painful, and you'll never get 100% there, but it also has the added benefit of being able to debug things locally too if something goes wrong with the pipeline.

The first time I used GH Actions I thought there was a strong vendor lock-in element to it which I wasn't hugely comfortable with. I'm a big fan of using GitLab CI these days which seems to be a good trade off between various considerations.