Is there any other way to purchase the Mac version? Steam stopped working for iOS versions under Catalina a while ago and as far as I can tell the game doesn't work for iOS versions past Mojave. 

Hey A99,
Mac version will be uploaded on Steam, GOG, EGS, Itch.

I recommend to read feedback of other players after release to be sure it'll work on your machine.
We will do everything from our side to provide the working version of the build. At any rate you can always return the game, if it doesn't work for you.