Do you have a “dock” bar along the bottom of the screen?
It’s one of those icons.
Or, you might try right clicking on the background and going into the properties for the display.
Cheers
Aha! I found it. It was in the Boot Camp control panel. The brightness was all the way down to “dim”, but the weird thing is I know damn well I didn’t open that thing before, so I have no idea who/what told it to dim itself.
Weird.