If it’s an application that can be launched by y2controlcenter or systemsettings (including those applications themselves) the error was thrown. I’m not about to make a list of them all.
I don’t know what went wrong, but if I had the game Windowed, of course I could drag it to the lower monitor. If I tried to fullscreen/borderless window the application, it would force on HDMI. X11 session always had placement on displayport, so if wayland kept it’s own settings separate, it always put the desired window as HDMI, regardless if I closed the window on the displayport monitor, it would reopen to those coordinates on the HDMI monitor.
EDIT: I’ve swapped to Wayland after making a snapshot to see if I could reproduce this behavior. So far it’s fine. I am unsure how these previous hiccups happened but will update as soon as I run into them.