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
That’s what it looks like to the untrained eye. But they’re not really going to fire a person out of a cannon. That’s not safe. So he just huddles in the cannon, they light a decoy fuse, it makes a bang (with no projectile), and he spring out and jumps that distance by himself. Requires a lot of core and leg strength.