I don't know if they've removed the ability to do it. I don't think you've ever had to do it. You can just hit space, or just start typing your password from the lock screen.
Yeah you can just start typing your password, last time I tried Ubuntu, at least. Or press any key, and the prompt should appear. Even pressing ctrl could work. But any character-key should be the key, in my experience.
I don't believe my 19.04 login manager does that. I do recall that being annoying because my first keystroke would actually just move that up. Now it starts up to the user list by default.
