Linux Mint 22.3 - computer lock & full screen demo not working

[dario.zip]

Hello, I have 6 computers all running Linux Mint 22.3. From my teacher pc I am able to see the other computers, send messages, remote control them.
But the mouse/keyboard lock feature does not work.
The same goes for full-screen demo, which I do need a lot.
Has anyone had the same problem?

All Veyon installs have been done through the terminal using
sudo apt-install veyon-master