on my benq xl2420z i use an dvi-d cable and i want to change the display settings on the screen it self, but the menu is turning grey so i cant change the display mode away from full.
Lower your desktop resolution to 800x600, it should no longer be greyed out. Incresae res back to your native, and it will force aspect ratio for everything below native.
Weird, all older monitors works when doing that, not sure why the manufacturers decided to stop. Try your graphics control panel, there's also an scaling option in there.
I have no idea then, works on my older monitors. Try to contact BenQ or try to find a different topic, or a different forum, maybe someone have found a solution for that.