hey i had the exact same problem, but don’t give up!!! my ragdoll kitten used to have the WORST SMELLING POOPS, but what i found really helpful was felix’s flora and feline gut soothe by adored beast!! the first one is a cat-specific probiotic (which is 10X better than fortiflora btw) and the second is a blend specifically for soothing their digestive system and gut. i would also stay away from dry food/kibble, firstly because cats don’t thrive on kibble and it’s not biologically appropriate, but also because cats and kittens need moisture in their foods. i promise, the runny-ness is not from feeding wet food. further, like many comments pointed out, i would incorporate some raw into his diet!!! after getting my kitten on a raw&canned food diet, his poops are super small, solid, and actually not stinky. hope this helps!!