Yes, I tried with VLC as well. It works as intended there. Video pauses, and the PC suspends or shuts down normally.
Firefox seems to be the only thing that prevents it, and only if there’s a video loaded. Doesn’t have to be the active window, and it doesn’t matter which display it’s on. If there’s a video playing or paused, it prevents suspend and shutdown.
I will check when I get a chance. Nothing jumped out at me after, but I didn’t think to check in the moment.