> The big problem with CI/CD on Mac is that Xcode does not allow you to run builds in parallel, so you need one Mac per build unless you use virtualisation.

Yes it does. The Xcode GUI only allows one build at a time, but you can run multiple `xcodebuild` command line builds using the same or different versions of Xcode in parallel, even under the same macOS user.

For running tests, there used to be problems if you were trying to invoke the iOS Simulator for different versions of Xcode in parallel, but those issues were fixed 4 or 5 years ago.

I've setup and used a set of bare-metal Mac mini CI runner, each configured to run two jobs in parallel, and the Xcode pieces of that are rock solid and didn't need _any_ workarounds to enable parallel jobs.