There are rare instances in which a Mac is required to build a version for macOS. Most game engines allow you to make Mac builds pretty easily.
There are only a couple instances I know of where you need a Mac:
- For code signatures and notarization (see: Notarizing macOS Software Before Distribution - Apple Developer)
- Your game engine does not support building a Mac version of the game
Like @ASecondGuy has said, if your engine has the ability to export to HTML5, you may want to do that if you’re worried that the Mac build will not work. Just a heads-up, though, that it may not work correctly in Safari on a Mac; I’ve tried playing many games online for jams, and it seems Unity WebGL doesn’t play nicely with Safari.