Mac is different on startup/sign in
When FileVault (System Preferences/ Security &amp; Privacy/ FileVault) is open to activate the mac you need to enter an administrator password or the recovery key (or Apple ID for reset). The password screen appears when you want to open either a non administrator, guest, or administrator user.
The username-password UI appears when opening the mac, to get rid of it turn off FileVault from System Preferences/ Security &amp; Privacy/ FileVault.

FileVault secures the data on your disk by encrypting its content
automatically.