Tub urination

Hello! So, my female cat has this awful habbit of urinating in the tub/sink, even though her litterbox is clean and ready to use. She is sterile. She still uses the litter box to defacate, and sometimes urinates in it too, acting usual, but mostly she just pees in the tub.

I tried cleaning the tub with different cleaning solutions, even those that break up enzymes, in hopes to get her to stop. I tried rewarding her when she used her litter box. I am out of ideas

Note: she didn't always do this. It started like a few months ago and she just kept doing it. There were times when the behaviour seemed to stop on its own but then she returned to urinating in the tub.

Did anyone else have this problem? Did you manage to fix it? If so, what can I do about this situation?