Already responded to your same question asked on their Discord server but, again...
Both Steam and Itch.io versions of the game are currently up to date with the latest released version. And Itch.io does have a downloadable version for Mac (and iirc the steam version should too, that is depending on if you have a macOS 10.14 or lower version) however, there's no key to get the itch.io version if you bought the steam version, and vice versa. So if you want to get the game on itch, you'll have to buy it on here in itch.io instead.