What model is your Mac? Where are you downloading the demo from?
AFAIK, the original Mac version of Anniversary was released for the old OSX... it's no longer a supported operating system, and if your Mac was released in the last decade or so, you can't expect it to work at all.
However, I can confirm that my iMac 4k (Late 2015) runs the Anniversary full game purchased from Steam absolutely perfectly
I imagine the demo uses the old code.