I just bought CRUMB on my windows pc, I then tried to download it on my mac, when I open it on my mac, it freezes, doesn't allow keyboard input, and flickers a pink rectangle across the window.
Yeah this happened for me as well. I downloaded it through steam and displayed a pulsating pink screen that would have been an epileptics worst nightmare.
Ditto. This is on a MacStudio M1 with 2 4K displays (3840x2160), running macOS 12.6 (Monterey). App launches and while in the foreground (full screen or windowed) the main display draws with toolbar, etc., and then a big, flickering magenta square in the middle of the screen. The in-window controls are inop, but the app's menubar responds to events to resize the window or quit. The problem is present regardless of other apps running, fresh reboot, etc.