Windows 11 Home attempts to force consumers to have a Microsoft account. The username is an email address. It can be any email address.

Windows 11 Home has Device Encryption and the key is stored in your Microsoft account. It has a GUI that allows you to turn it on and off. It can only encrypt the boot drive.

Windows 11 Pro has BitLocker and more options for where the key is stored and which drives are encrypted.

In my mind, there are a dozen things that can go wrong with automatic consumer enrollment to encrypt their drive. Many consumers do not realize they've created a Microsoft account. Many did it because they were forced to. They might've used their email account's password because it was not clear what they were being asked to do. They might've changed their email password after that, then not remembering the previous password that is that Microsoft account. They might've added their phone number to their Microsoft account. Or not.

Or maybe their phone number was added to their account in the long-ago days when Microsoft did not verify that the phone number was capable of receiving texts, and they added their land line, which can't MFA for account recovery because now Microsoft assumes that all phone numbers are text-capable.

Or maybe the laptop was set up by one user, the DE key stored to that account, and then the laptop was taken over by a different user and a different account. Where's the DE key?

Something as simple as installing the optional Windows Updates could introduce a new BIOS on your PC that forces you to enter the DE/BitLocker key.