Hi there, the very best thing to do is reduce/ remove stress. Are there other pets, children, neighborhood cats around? Is he allowed outside?
Read up on body language to help recognise when things aren't going well for him. Staring, spraying, going outside of his litter tray, another cat in his territory, a change in diet, stressed owners, not being able to get either high up or in a safe cave....
Has anything changed in his world? House move, air fresheners, different detergent?
When is he happiest? Do more of that!
Keep all resources separate. Food, water, litter all at least metres away from each other. Ideally different rooms. Ideally more than one source for each.
Also worth looking up how to help him wee 😥