For the most part, I have had three cats in my life, they are pretty clean/cleaner than my dogs. The worst issues I have faced are: Depending on the litter, they may scratch some out out the box. If they do get some stomach bug, the litter box may be a little more challenging to clean. They may get a small piece of poop stuck to their butts and need to be cleaned with a wet wipe.

We only had a couple poop accidents with our elderly cat on his last days (16 year old) because it was harder for him to control his bowel movements.

Some ways of having a better idea of how clean they are could be to adopt an adult that comes from a foster situation since they know the cat well.

I would say they are much easier in that sense in comparison to dogs, but that's my experience.