When switching an application to full screen the monitor turns black for a couple of seconds. Reinstalling drivers and resetting the BenQ monitor didn’t help.
The solution was to change the refresh rate of the monitor from 59.94 Hz to 30 Hz. To do in Windows 11 go to Settings => System => Display => Advanced Display and switch “Choose a refresh rate” to 30 Hz.
UPDATE: the used cable doesn’t support 59.94 Hz or 60 Hz, so switching back to 30 Hz did the trick.