@tatanas Any chance you can test with the internal VNC server and disable the external UltraVNC server instance temporarily? That would allow us to figure out whether your issues are related to the external VNC server feature in Veyon.
@makerspacelab I have good news for you: this feature will be implemented in 4.6.1. If you already want to test, you can download and install the current test build at https://github.com/veyon/veyon/releases/download/v4.6.0/veyon-4.6.0.32-win64-setup.exe – besides messages being selectable/copyable student-side, it's now also possible to copy rich content, i.e. formatted text including hyperlinkers.
Veyon also works without AD. In this case it's recommended to use the key file authentication method if you are connecting to multiple computers/servers since otherwise you'll have to create identical accounts on all computers.
May you have some hidden special (e.g. UTF-8) characters in your file or some kind of encoding or newline problem? I was able to run the command with the given example file without any problems 🙂