Wanted to send this through a direct message, but there wasn't any way to.
Picked up a copy and sent this to a team member working on MacOS, and of course it didn't work.
The Mac version of Pixel FX Designer doesn't work with modern MacOS, or even with a lot of older setups. I get that keeping things working on Mac requires constant work from the developer, and that probably doesn't make sense from a developer perspective to keep updating this program. You just really should delist the MacOS version, because as it stands now you are just implicitly lying to users that "oh yeah, totally runs on Mac my guy" when it just doesn't.