It just says it can't open

A fix for that can be to launch it via the desktop client. The Itch.io client.

I have the error that I don't have a programm to open

You can open it using the Terminal. You can see how to do that a couple treads back.

https://itch.io/t/708555/macos-karlson-fix

i spent way too long on that lmao. thank you for that !