Catalina 10.15.8 update fails on MacBook Air 2012
The update is not installed Mac OS Catalina 10.15.8 MacBook Air 2012
MacBook Air 13″, macOS 10.15
When exactly is it failing? Before it restarts? During installation (black screen)? During download?
Does it issue an error? If so, what does the error say exactly?
You might want to try to update in Safe Mode:
Start up your Mac in safe mode - Apple Support