The mysterious password prompt
Starting in macOS 10.15 (Catalina), Apple started requiring a password to do anything useful after booting into recovery mode:
It’s not exactly clear what this password is for. T2-chip Macs have hardware-based encryption, and that encryption is able to turn on instantaneously. Without mounting the encrypted drive, you can’t really reset a password or have access to the data on the drive. This prompt just seems like a rather odd choice, especially since it appears to act as almost some kind of firmware lock… except it’s not.
Option 1: Erase without password or recovery key
If you don’t know the password to a user account and also don’t know the recovery key to FileVault, you can still use recovery mode to erase the current installation and reinstall macOS. Yes, that’s that menu item hidden in the top-left corner.
You can just click Recovery Assistant and then select Erase Mac….
You’ll then be prompted to join a wireless network, and then some kind of Internet recovery is downloaded and booted to, and then you’ll be back at recovery mode with a prompt to activate your Mac, and then with the opportunity to reinstall macOS on the freshly wiped drive.
Option 2: Use FileVault recovery key with no password
But let’s say you don’t want to wipe the drive necessarily—you just want to do other recovery mode stuff, and you don’t know any user passwords. Well, you can click Forgot all passwords?
Then you can enter the FileVault recovery key for the drive.
Option 3: User FileVault-enabled user password
And if you do know a user password, of course, you can select the user, and then enter a password when prompted.
The only odd thing about that is it doesn’t actually get you past FileVault encryption.
That’s right. Even though you’ve entered a user password, if you want to mount the Macintosh HD – Data partition, you’ll still be prompted for a FileVault-enabled user’s password again.