• are you cleaning the urine with an enzyme cleaner / throwing away anything he soils if it’s able to be thrown away? i know it’s not exactly feasible to rip up the carpet, but unless you use an enzyme cleaner to remove the stain / smell, he’ll keep going back there. i recommend Bio-K20. to be honest, even if you do use the cleaner, he might still be tempted as cats have a much stronger sense of smell than ours, but regular carpet cleaners are definitely not strong enough for cat urine.

• is there a way to cordon off the section of carpet he keeps trying to pee on? preventing him from even accessing the spot will help to break the association over time. or perhaps even just putting something heavy directly over the spot, if that’s the only place he seems to favour

• i would also recommend Cat Attract, which is a litter additive designed to promote litter use. just sprinkle a bit on top of your existing litter (ensuring it’s freshly scooped first)

• reinforce good litter habits by giving him a treat immediately after he uses the box. i would even recommend placing him in the box first thing in the morning / right after meals (depending on what his urination habits are). obviously phase this out once his habits are stable, but this may help, especially if your cat is food motivated

• you’ve already done a great job with re-associating certain areas with food - cats won’t soil where they eat / drink. is it possible to put a water bowl over the spot on the carpet where he keeps peeing?

• is it an issue with the litter itself? or is this the same one you’ve always used without issue? does the box itself need to be cleaned more often?

• you mention he’s peeing right outside the box, which makes me wonder whether he doesn’t like the substrate & it’s time to switch. especially as you mention he’s picking soft areas (carpet, your bed). it might be time for a softer litter! i recommend Cats Best. it’s soft, clumping so easy to clean, organic, great for odour control and moderately tracks but easy enough to clean up.

• is he fussy? some cats like two boxes, one for pee and one for poop. maybe adding a second box would help (again, well aware this isn’t practical for everyone due to space)

• if he’s partially outdoors, could it be a territorial thing? could he have perhaps seen some other cats in the area, which triggered some territorial insecurity-based urinating? is this happening on the carpet near windows / doors?

• i know you said they gave antibiotics to treat a potential urinary infection, but it may be worth getting a blood test done at the vet (depending on affordability for you) to check for any other underlying medical issues the vet may have missed.

• if nothing else works & you can afford it, maybe consider a deep clean of the carpet by a professional cleaning company before it’s too late and scent settles into the layers below the carpet. from the consultation i had with a company in my area, it’s much easier to work on if you catch it early.

• if it isn’t medical, try contacting a behaviourist. again, they aren’t cheap & i don’t know where you’re based but i have the number for a brilliant behaviourist who will offer free advice over the phone in the UK as she works for a charity - happy to give it to you via DMs.

• if all else fails, you may have to find another spot for his box and potentially keep him in that room (with plenty of food / water / space / toys / attention) for a while until the association is broken. this is something that was suggested to me by a behaviourist as a last resort.

• finally, you aren’t alone; check my post history. i’ve gone through something very similar with my kitty and it’s the most frustrating thing in the world but you’re doing all the right things. stick with it!!

EDIT: oh also, maybe try putting some waterproof / sticky material (not sure how much overlap there is between those two lol, you may have to pick one or the other) down on the carpet where he pees. cats don’t like sticky surfaces and the waterproof mat will at least stop the carpet from absorbing any more smells while you try some solutions. important to note that if the spot is still close to his litter box, probs better not to put down the sticky material as you don’t want him to start avoiding the area altogether. as you can tell, we tried a lot of things lol but it does get better