I know it does but you said “That kills the point of LibreTube bruh.” So if you can use a VPN, and there’s no point to slowing it down…it doesn’t sound like disabling it “kills the point” at all, like you first said.
Basically, your two messages contradict each other.
I’m not on Debian, but a quick search led me to this wiki link from Arch. Give it a whirl:
https://wiki.archlinux.org/title/GDM#Hide_user_from_login_list
Edit: context of the Arch wiki link, in case better answers can be gleaned from it, I found it on AskUbuntu: https://askubuntu.com/questions/2471/how-to-hide-users-from-the-gdm-login-screen