Hi there and sorry for the late reply, I don't usually check forums but I'll do it more often from now on.
I've just replied to a similar post the steam forums with more information about this issue, please check it out: https://steamcommunity.com/app/939360/discussions/0/1743354432805978364/#c174223...
As a TL;DR: I can't fix some bugs for the OSX version due to the engine where Pixel FX Designer was made having some functions that simply don't work on any other platform than Windows. I'll be contacting Steam so we can provide refunds for OSX users that went over 2 hours of use of the program.