A logic issue was addressed with improved state management. This issue is fixed in macOS Big Sur 11.6.2, macOS Monterey 12.1, Security Update 2021-008 Catalina, iOS 15.2 and iPadOS 15.2, watchOS 8.3. A local user may be able to modify protected parts of the file system.
https://support.apple.com/en-us/HT212981
https://support.apple.com/en-us/HT212979
https://support.apple.com/en-us/HT212978