Big Sur upgrade issues - Admin removed from main/only user
My wife has upgraded her Macbook Air to BIG SUR but now has No admin user and .AppleSetupDone file not found when trying all the fixes we see on line. As many of the apps updated to their 64-bit version she cannot customize anything because she keeps getting asked for the Admin ID and Password. As we cannot fix this with all the different methods given by helpers here, can we take the 2014 Macbook Air to Apple store and have them fix it at NO CHARGE as it Apple's fault this has happened?
MacBook Air 13″, macOS 10.14