I am using Windows 10 Home 20H2 with the lattest update. My second monitor died and I disconnected it. It had a VGA cable connected to an HDMI adapter and plugged into an RTX 3060.
After restarting, my screen is split into two panes, left and right. There is a vertical bar with two dashes that I can drag around. It seems that Windows is sort of behaving like the split screen functionality, but with several differences from what I have seen in videos:
Now all or my windows are aways fully minimized or fully maximized and taking over one of the two panes, I can't adjust their sizes anymore.
I can't see my desktop. Does not matter what I do. If I minimize all windows, all I can see is the start menu taking over all of the screen space, even though the full screen option for the start menu is deactivated in settings.
My windows don't drag freely as I have seen on some videos, a miniature of them under my cursor just drags straight left or straight right, as if on rails, and then expands to fill one of the two panes.
Turning Snap Windows off on Settings>System>Multitasking disables my ability to have two windows side by side, which just worsens functionality and does not solve any of the previous three issues.
I have PowerToys installed. I killed it in the task manager, but it does not seem to be causing this.