MOONSHIRE is officially playable through Steam with MacOS! Keep in mind that Steam (and Apple) only support 64-bit operating systems, so anything earlier than MacOS 10.15 may not be able to run the game. Here is Steam's official statement on this:
https://help.steampowered.com/en/faqs/view/743F-2E0E-C9A5-C375
If you encounter any issues, please let me know!