Happened on P14s on Ubuntu 23.10, which started with fresh Ubuntu 23.10 install.
However it did not happen on Lenovo ThinkPad P51 (2017) also on Ubuntu 23.10 which had been upgraded several times from God knows what starting point... At first one had X11 (forced by Nvidia drivers) and the other Wayland, but moving to p14s X11 changed nothing.
Both were running GNOME Display Manager.
Same happens with Super + L, but also CLI commands: askubuntu.com/questions/7776/how-do-i-lock-the-desktop-screen-via-command-line
Bibliography:
- askubuntu.com/questions/1242110/after-upgrading-to-ubuntu-20-04-lockscreen-not-working canon
- askubuntu.com/questions/1246622/ubuntu-20-04-unable-to-lock-screen
- askubuntu.com/questions/1245071/cant-lock-screen-with-shortcut-on-ubuntu-20-04-gnome
- askubuntu.com/questions/1248756/super-l-not-working-on-ubuntu-20-04