We have a cat now that is inside only. Our last two cats were inside/outside cats that we had for years, but months apart- each of them went out one night and never returned (we pretend some nice family took them)- they were probably eaten by coyotes, and owl or whatever....we didn’t want that to happen to this one too (the nice family taking cats fantasy was wearing thin) so we keep her strictly inside.
If it’s a litter box factor- maybe look into those electronic cleaner ones that sweep the litter after use. I’ve never bought one of those but it could work.
I use for my indoor cat “Feline Pine”.....It smells like cedar, you never ever smell the urine and it last for weeks.....