> Also, somehow that bar can show what's on each virtual desktop, and in real time, so I know that's at least possible. That bar shows a small lower-res previe

> Also, somehow that bar can show what's on each virtual desktop, and in real time, so I know that's at least possible. That bar shows a small lower-res preview of each of the desktops, it is not rendering all the desktops at full 4K res. Essentially the smaller a window appears on the screen, the lower effort is needed to draw it.