Embarrassing to admit but I’m now starting into hour 3 of trying to upgrade my wife’s MacBook Air from Big Sur 11.2 to 11.3.1.
I’m using Software Update.
It either downloads the update again (I’m not sure if prior downloads are on the Mac) or it finishes the download and then hangs on “Preparing to Install” at 15 minutes remaining mark.
Will Apple release another upgrade that might work better?
You don’t say how long you waited for the “hang” to resolve itself, but others have reported updates taking an hour or more, depending on their setup.
The 11.3.1 update was a security fix, so it’s a bit more important than some others.
Rumor sites say the 11.4 update will be released early next week.
It’s very doubtful that any remnants could cause problems.
You should be able to completely erase and install 11.3.1 from Recovery or by creating a bootable USB drive with the 11.3.1 installer on it. Apple has articles on both solutions. About Recovery. How to create a bootable installer for macOS.