@Mad_Ark_Nbg
Whenever you update your Mac’s OS, the update reverts some of your app preferences to the default settings that tightens user privacy.
For Zwift, this means you have to manually re-allow Zwift permissions to write to the Documents folder. If you don’t, the game can’t run properly. How-to’s on this Support Hub page, which says it’s for macOS Catalina, but the same applies to macOS Big Sur
Would you try that and let us know how this worked? We like to hear an affirmative yes / no.