I changed user UID and GID from 1000 to 500 using usermod and groupmod. sddm.conf, login.defs and adduser.conf changed for MIN/FIRST user UID. System works great, but my user is no more listed in user-manager.
I wonder if there's any way for us to make user-manager notice this change. If not, maybe we should add a GUI setting for this in user-manager itself to provide a safe way of doing it.
AccountsService takes the minimum UID at build time from meson_options.txt option('minimum_uid', type: 'integer', value: 1000, description: 'Set minimum uid for human users') If you change from your distro settings, you will need to rebuild this to match. If you think this is an issue, please take it up with accountsservice on freedesktop.