No, you’re confusing MacOS with iOS. Mac allows whatever you want. Each browser has its own rendering engine. iOS is the one that only allows (for the moment) Webkit. But that’s going to change (at least in Europe). Here: https://en.wikipedia.org/wiki/Comparison_of_browser_engines#Support
Mac literally doesn’t allow any other browser engine. They only allow webkit.
So your options are:
Safari
Safari with Chrome aesthetics
Safari with Firefox aesthetics
Safari with [insert browser here] aesthetics
No, you’re confusing MacOS with iOS. Mac allows whatever you want. Each browser has its own rendering engine. iOS is the one that only allows (for the moment) Webkit. But that’s going to change (at least in Europe). Here: https://en.wikipedia.org/wiki/Comparison_of_browser_engines#Support