Sometimes cats do things that we, as humans, have a hard time understanding. The underlying cause for these behaviors is often related to instincts left over from their wild ancestors.
a lot of cats display this behaviour. It could just be because he goes to check out what you are doing, and then boom! What a good idea partner, lets use the litter box.
When my cat was young she used to do this every time I clean the litter box and I clean it once daily. However she stopped doing it after I started telling her ''No'' every time she tried to do so.
She still likes to come see me clean it every time but she doesn't go in. She waites until I'm done then gets in. It could be due to the fact that cats know the litter box gets clean and fancy after we are finished cleaning it, and so try to make things faster by just using it already even before we are done cleaning.
Some cats steal almost any object they can get their paws on. If your cat receives attention from you for stealing things - even if it's negative attention - it may teach her to continue doing it. Another possibility is that it's a form of play. If you think this is the case, try providing something else for your cat to do, like feeding puzzles, toys to play with, or, even better, establish a playtime routine. This might alleviate any boredom that causes her to get into trouble.
Your cat is depressed
Remember how you felt the last time you got dumped? You stayed in bed all day, didn’t change your clothes, and ate only when your mom called and insisted that she was going to come over if you didn’t shove some food into your face right now.
A cat who has lost a beloved companion might behave similarly. He leaves his food untouched for days, ignoring even treats. He hides under the bed. He is indifferent about grooming, because “sigh” what’s the point? And he sleeps even more than his usual 18 hours per day.