I'm running a 2008 Mac Pro cheesegrater, running High Sierra.
Depending on what engine the game is in, it will simply require the export of a mac binary....
Then memory optimisation will be the only problem.
This is not true. No engine can develop for macs without going through Xcode. It's possible to build a game on some engines that will run on your own mac, but other users will be unable to install your game unless you have an apple developer certificate. This requires the developer to be enrolled in the Apple developer program, which has a monthly fee associated with it.