On both my iMac and Macbook I get the following error:

You do not have permission to open the application “TuxAndFanny”. Contact your computer or network administrator for assistance.

System details:

iMac: macOS Big Sur Version 11.5.2 iMac (Retina 5K, 27-inch, 2017)

Macbook: macOS Big Sur Version 11.6 Macbook Pro (15-inch, 2018)

Any solutions?

Hello and sorry for the inconvenience. I believe this thread has links to two solutions that usually work, as well as a video walk-through for both of them. https://itch.io/t/1777652/video-fixing-tux-and-fanny-for-mac

If you're still having issues trying to get the game running after that just give me a shout.