My kittens about 22 weeks old and has never used the litter box. I’ve never have a problem with the mom I would have thought he would have learned from her but no. I’ve tried literally everything from smaller litter box, two litter boxes at opposite ends of the room, different litter, put him in there 30 minutes after eating and sleeping, with/without hood, keeping it clean etc. I can go on for hours I’ve read just about every article on this subject. It use to be in the bathtub then started keeping the door closed then he started in the hallway then stopped but has always gone in the room where the litter box is and he’s finally down to just going in that room. I’ve cleaned the carpet after every time but now it’s just gotten to hard to keep up with I have to replace the carpet now and have just picked up the poop and spray the area. if anyone has any help please!
Disclaimer: I'm not a vet, just an experienced cat owner.
Cats are focused on scent. It could be that your continuous cleaning is taking away too much of his scent and not allowing him enough time to take ownership of the litter box, so to speak.
First, I would definitely advise you to get a cat litter mat to save your carpet.
Next, you might try placing the poops you find next to the litter box inside of it. Leave them there long enough for him to find them the next time he has to go.
If you still can't get him to use the litter box, it's worth taking him to the vet. There might be some other, physical reason why he's not using it.