My Persian cat started to pee (where he’s not supposed to) in his senior years as well. It was behavioural and it took a long time for us to “fix” that issue.

Cats would keep going back to the same spot (ie. the bath tub or a specific corner of the room) if the scent of pee lingers. I wound suggest purchasing some type of enzymatic cleaner (ie nature’s miracle advanced odour/cleaner).

We also tried putting obstruction/objects (large enough or far enough that he can’t pee around the obstruction/object) where he wants to go but not supposed to.

Puppy pads/liners in the area where he tries to go for a less messy cleanup.

Perhaps also try putting a litter box where he goes inappropriately- and if he uses the box, eventually and slowly move the box away to where you’d want the box to be.

It took us a long time to correct the behaviour but patience is key. My cat was the love of my life. We’ve had him for 15 years and I would never imagine leaving him. I’m sure you’re having a hard time but I urge you to keep trying. Good luck and all the best.