I recently added an external monitor to my Debian 12 laptop, setting it as the primary display while using the laptop’s monitor as secondary. However, I’m experiencing an issue where the external monitor randomly goes black, while the laptop screen continues to display normally. Moving the mouse brings the external monitor back to life. Interestingly, this happens while YouTube is running, with the audio playing uninterrupted. So far, I haven’t noticed this behavior with any other applications.
Update: I was running YouTube from within the Firefox browser, not a YouTube app (If one even exists)
Try seeing if your monitor has any weird power settings. I’d imagine it’s not a monitor problem, based on it turning back on after mouse movement, but perhaps it improperly responds to some message sent over the cable.
Speaking of that, what cable are you using? Is it HDMI or Displayport, and does the laptop have a full port or are you using a USB adapter?