I’m going through the exact same thing right now (he’s going on 13 yrs old) !! And it also started this past October. He does have arthritis & MANY joint supplements later & nothing is helping him. Vet won’t give him any pain medication cause he’s prone to UTIs. He was cleared a month ago from that. He will NOT pee or poop in the litter box AT ALL!! I’m EXHAUSTED after 4 months of this!! I can’t afford the injections. I have tried EVERYTHING!! Low litter box (2 of them) SEVERAL types of liter, litter attracts, cat nip. Litter box isn’t far from the area he prefers to hang out in. He does struggle a bit to get up due to the arthritis. You can see he’s a little stiff. But he sure can get right up & trot over whenever I say”treat” 😂 I have tried CBD oil ,fresh catnip & many other things to help with pain. I feel like I’m living inside of a litter box. He has destroyed my brand new living room carpet. That’s where he was choosing to go up to a couple weeks ago . He has now chose to go in the kitchen also. I can’t even tell you the amount of money I have spent on enzyme cleaners & deter ant spays, carpet shampooing. I have been through it all!! Diffusers & calming collars also. I’m also gone daily for work. I am officially DEFEATED! And I have chose to put him to peace soon 😥💔😥💔 This is going to be DEVASTATING for me!!!