[GordonS]

Azure DevOps also has a generous free tier with lots of CI minutes, and I'm fairly sure you can use the MacOS pipelines in that tier.

I've used Azure DevOps on several projects, and it's CI/CD capabilities really are fantastic.

I've also used AppCenter (and the previous incarnation, HockeyApp), and it makes for a great app distribution experience. It also has an integration with InTune, which is very useful in the enterprise, although we did find configurating it to be a total PITA and it required a domain admin to set it up.