The problem is that when macOS is set to prefer tabs, Android Studio 4.1.1 on macOS Big Sur also opens things like branch settings in tabs instead of windows.
To fix it, you can prevent those tabs only in Android Studio.
Open Terminal and run this command:
defaults write com.google.android.studio AppleWindowTabbingMode manual
Now Android Studio will use windows again and not crash.
Solution was found on reddit https://www.reddit.com/r/androiddev/comments/jtbl4m/has_anyone_updated_to_macos_big_sur_and_is/gc8pfhg/?utm_source=reddit&utm_medium=web2x&context=3