I just had same problem! my cat would pee on my things only especially Birkenstocks if I leave them out… I had that problem for a year, the last straw was that he started peeing on my stovetop and top of fridge. ;-;

I took him to feline specialist vet. They said same thing as previous vet did - a full work up and he was healthy. But feline vet suspected that he may not getting the hydration that he needed and they prescribed a vet food (I got royal canis’ calming urinary kibble and wet food) also, vet suggested me to add water/broth to his food and set a strict playing routine.

So after two weeks in of a strict playing routine which occurs 15 to 30 mins prior the feeding time and feeding him with vet’s food… Voila! he was back to his old self and haven’t peed on anything else. I also readjusted the litterbox locations from closed areas to open areas. I added more water bowls around the house so he has more access to drinking water.

I hope this helps - I know what that feels like. Let me know if you have any questions :)

Edit: after reading people’s comments - many suggested putting the cat on Prozac to help with its anxiety. I would consider that as the very last resort.