Classic WoW not launching when using external monitor

Good morning
currently i have the following problem - lately i have connected an external monitor to my laptop. I want to use this as the only monitor so it is set as the primary monitor.

The laptop monitor is disabled.

So, now I try to start Classic WoW - the monitor goes black for a moment, I see that the cursor changes to the WoW cursor and then WoW crashes.

If I now enable the laptop monitor and set it as primary monitor and start WoW, it works - even if I tell it to start the game directly on the external monitor in the WoW settings.

I use “Ubuntu 22.04.3 LTS with Budgie”.

Does anyone have any idea where I should start looking - it’s driving me nuts…