I have my laptop connected to an external monitor with a hdmi cable. The display is "extended" with the external monitor set to be the primary display. When I disconnect the hdmi cable, the laptop should detect it was unplugged and switch back to one display, the laptop's display. This is how it has worked for months.

However, recently the laptop has completely stopped detecting when the monitor is unplugged, so I'm left with a laptop that thinks it's a secondary display. I can't see the taskbar, or if I open display settings it opens on the external (main) display that doesn't exist anymore. I have to use shift win left to bring the settings window over to the laptop display and then select "duplicate these displays" . The 2nd monitor is still displayed in the little graphic and clicking "detect" doesn't change anything.

Any ideas how I can get the automatic switching back?

Windows 10