I never knew this was an option. I was viewing a video from Finder in QuickLook. While jumping back and forth between apps, I accidentally hit Cmd-L in Finder when I intended to be in Safari (to copy a URL). The video rotated left. Cmd-R, predictably at this point, rotated back to the right. I assume images would work as well, but the video hasn’t finished playing so I haven’t confirmed.

I’ve been a Mac power user for decades and this was a satisfying discovery.