one time i was testing something with the monitor in the motherboard, which worked fine, and then i put the gpu in the motherboard but forgot to plug the monitor in the gpu, and it showed a black screen.

there might be systems where you can plug both a gpu and the igpu into the monitor and it’ll use one for most things and the other for games and stuff (i dont remember what that is called), but i have only ever seen that in laptops so idk