Cat is obsessed with bathroom- please help!!!!!

My partner and I moved into a new apartment around 6 months ago. It is spacious, has plenty of entertainment for the cats, litter box, windows, food and water. They have everything they need easily accessible to them. The one room they are not allowed in is the bathroom as there is a window that does not close and we don't want them to escape. They've never been allowed in the bathroom. They've never been in the bathroom. They've never seen inside of the bathroom. There is no reason for them to have any interest at all, and 2 of them don't care.

However my cat, who I've had for three years, will not, cannot leave it alone. Every. Single. Night. he sits by the bathroom door and screams for hours. It's driving me crazy. I can't sleep. Its disrupting my performance at work. Its making me a cranky asshole. Its affecting my partner's sleep and our relationship. Nothing distracts him, nothing satiates his need to go into the bathroom. Its starting to happen in the day time too. I have taken him to the vet, and his bowel movements are normal. I try to give him attention and he does not want it. I play with him before bed and while that seems to have some effect it doesn't stop it. I've tried calming and cbd treats but he does not eat them.

What does he want? How do I help him feel less aggravated? I am reaching my limit with this behavior, it is seriously affecting me. Please give me advice, or wisdom, or ideas or something to help with this behavior. I love him so much and he has gotten me through some very rough times in life and I want him to feel comfortable in his home, but we cannot continue on like this. Please help me.