Keep holding Win and tap P to cycle through: PC screen only: Turn off the external monitor Duplicate: Show the same thing on both screens
Ensure apps managing your windows have Accessibility permissions enabled under System Settings > Privacy & Security. If you want to optimize your setup further, tell me: What operating system do you use most? How many physical monitors do you have? switch screens shortcut
He rebooted. Updated drivers. Ran diagnostics. Nothing. Keep holding Win and tap P to cycle