Could he have a hearing problem? Lops are prone. Deaf/hard of hearing buns can get scared easily by things they see, typically fast moving things, because they can’t hear them coming. By choosing to stare at the wall he could be trying to eliminate scary visual stimuli?
Lops are prone to ear infections, which can heal on their own so the owner never notices. Ear infections can cause destruction and scarring deep inside the ears, and that causes deafness/hearing issues. It can be one ear or both and an infection could have happened years ago.
Deafness/hearing problems in humans can mimick dementia. Animals generally do better than humans though, because they’re not at all as reliant on communication via words.
Animals can get cognitive issues in their old age, but your bun isn’t geriatric.
That said, rabbits have a transparent third eyelid that enables them to sleep with their eyes open. So he could be napping. It can be scary for the human, the bun looks awake, but is actually sleeping.