First, I swear this is not a very late april fools joke.
I have a multi monitor setup: 2 iiyama G-Master GB2788HS (27", 144Hz) connected both to a NVidia Geforce RTX 3080.
My problem is with VLC fullscreen (either video or streams, doesn’t matter). When I fullscreen a VLC window (double click or press F) on any monitor, it sometimes goes black, sound still playing normally. Moving the mouse still displays the controls, so the problem is not that the monitor doesn’t display anything. Removing fullscreen displays the stream/video normally, so the problem is exclusively while fullscreen.
Now, when I say “sometimes”, that is because I cannot in very definitive terms express when this happens. I can reproduce the problem in the following way: Open a stream/video in VLC, maximize it on monitor 1 (plays fine in fullscreen on monitor 1), normalize (removing fullscreen), move it to the monitor 2, then fullscreen on monitor 2, and the fullscreen image goes dark. I’ve had the problem on monitor 1 as well, after having maximized a video/stream on monitor 2, but that is more difficult to reproduce.
My current workaround is closing the stream/video down, then restarting. VLC remembers which monitor had the VLC last, so it reopens on the monitor where I closed it last, then fullscreen, and that always works.