My iphone 14 pro max has the exact same issue. It’s a used one and I do not know if the previous owner replaced the screen. When AOD is on, the screen brightens up normally when notifications arrive. But when AOD is off only the sound and vribration come through, the screen remains off.
Also, “Hey siri” does not work. Only when I tap the screen so it lights up, or with AOD on will Siri respond to my “Hey siri”.
Another problem with my 14PM is that the screen has a delay before turning off during call when I put it close to my ear. And when I take the phone off my ear, the screen cannot turn back on unless I press the power button or rampantly tap the screen, which is really frustrating.