Not new to photoshop - however new to this problem. It refuses to open any gifs, and I keep getting a popup that says "Could not open “filename.gif” because of a problem with the file-format module interface." I've tried resetting my preferences, updating photoshop, allowing full access via accessibility settings, renaming and resaving the file, and making sure my mac is up to date.
If it matters - I run photoshop 2021 as well as macOS Big Sur 11.2.3.
The Creative Cloud app allows for multiple versions of Photoshop to be simultaneously installed. Can you open GIFs in another version? This could help isolate whether the problem is with a specific version of Photoshop or something else.