I have just bought and tried launching the game, but also ran into a variant of the Mac issue. I experienced the same behaviour with both the standalone Stacklands.app and launching using Steam. v1dra's fix was necessary to launch the standalone app. This is Stacklands v1.0.11 on macOS 10.14.6.
Upon launch, the Sokpop animation runs but slowly. Right after, in the game menu the game freezes with very high CPU usage. Because it's full screen by default, there is no way to exit, and the only way out is a hard reboot. Unpleasant!
Such a large spike in CPU usage quickly paralyzing the computer is symptomatic of a "while(true)" loop without break or with insufficient sleep time.
I'm looking forward to hearing an update from the devs. Please run tests on a Mac before each new version release... or stop claiming that this game is Mac compatible (many games are correctly advertised as Windows-only).