This issue was addressed through improved state management. This issue is fixed in macOS Tahoe 26. Incoming FaceTime calls can appear or be accepted on a locked macOS device, even with notifications disabled on the lock screen.
A logic issue was addressed with improved checks. This issue is fixed in macOS Big Sur 11.6.8, macOS Monterey 12.5, Security Update 2022-005 Catalina. An archive may be able to bypass Gatekeeper.