See GitHub Docs: About billing for GitHub Actions for context.
Running GitHub-hosted runners with macOS is inefficient, especially because it consumes x10 more free minutes than running a job on Ubuntu-based runners. Thus, unless the use of macOS is inevitable, it might be better to use Ubuntu-based runners instead.
The above only applies to private repositories. But still, it is also true that there is no reason to stick to macOS as well.