How do I set English only in GDM?

Desktop
1

I have 2 languages in the system, but my password is in English, I want only English in GDM, even if there is another language in the session.

2

This is kind of a workaround, but if you create a second user account, then Settings will have separate configuration for the login screen in the Region & Language panel.

It kind of sounds like you may be asking about the keyboard layout though, which is separate. Settings lost the ability to configure the login screen keyboard layout at some point, but you can use localectl, e.g. for QWERTY:

localectl set-x11-keymap us
3

Or if not, change your password.