Actions does seem to be winning, but having used both extensively I'm convinced that it's on name recognition alone (with pricing being a second). Gitlab CI is my favorite of the many I've tried (gitlab, circle, travis, github), Actions is probably my least preferred. It gets the job done but there are always a lot of actions-specific stuff for every job, whereas with most of the others they're relatively portable. Actions feels like it was designed with lock-in as a primary goal.

GitLab CI can launch multiple pipelines on the same push/trigger (use separate files, like GH Actions, etc), but even after using it for I don't even know how many years I'm still struggling with setting it up in a nice way.