I've had a Mac for years now, and I used to customize a lot the way the login screen and filevault password used to work on my device.
Recently, I had to handle it to the Apple Store for a logic board replacement, and they nuked my drive in the process. I was on macOS Mojave before that, and I always have a clone of my disk ready for that sort of issue.
So when I got the machine back, I plugged in my USB clone, booted on it, provided filevault password and cloned this disk to my internal macbook pro drive.
Everything went well, but now the way the login windows behaves has changed.
Before that, when I booted up my Mac, I was first prompted for the Filevault password, with a screen that said "Disk Password". Once I provided this password, a progression bar appeared and when it was completed, a new login window appeared with fields for both username and password. Nowhere in the process my username was disclosed in any way to the user, and that was exactly what I wanted.
Now, when I boot up my mac, I'm only asked for my password once, and the username is displayed on the login screen. I understand that now my account is both decyphering my disk AND login me in, but does anyone know a way to have the "old" behavior back ?