It's unlikely that there'll be a direct Mac port any time soon for the reasons that Gregor stated: OSX support (both in terms of graphics APIs and graphics drivers) for gaming is very out-of-date, and Planet Coaster is making direct and copious use of features that aren't readily available on that platform. The most popular Mac alternative is OpenRCT2, which is both free and Open Source. If that doesn't suit you, our users have ranked 5 alternatives to Planet Coaster and three of them are available for Mac so hopefully you can find a suitable replacement.