The Meta Quest 2/3 finally fixed that a few months ago [1], where you "tilt" the horizon of the entire OS [2]. So it doesn't matter if an app doesn't support it -- you can lie on your bed and watch a screen directly above you even if it was only designed for horizontal use. It's a game-changer if you have back/neck problems.
Does the AVP not have something equivalent? To be honest, I was surprised it took Meta so long to get around to implementing it.
AVP doesn't support it when in 'theater mode' but if your video is a typical window you can simply lie down and recenter it onto the ceiling. The horizon stays locked but any windows can be parallel to the ground.