I'd like to add another idea in addition to the other answers. I'm coming from the perspective of a dog owner so please take that into consideration.
My cattle kelpie is now 16 years old. He was hospitalised after a severe spinal injury almost three years ago. After the hospitalisation and during his recovery period he was very sensitive to food. We reacted by making sure his food was thoroughly cooked and every aspect of our preparation and his eating was sterile. He's suffered from digestive issues over the last one and a half years that have manifested as long and severe bouts of diarrhea and "jelly" poo, which is sad. A number of carefully controlled diets failed to solve the problem.
The first hint of the solution came when the vet prescribed calf scour tablets. This medication was developed to stop baby calves dying from dehydration due to diarrhea. The symptoms are usually associated with poor gut health. We continue to treat our boy with a quarter tablet every three to four days. It helped a lot.
The next step was to feed him natural, mostly raw food. This was to encourage his body to produce the correct proteins in his bile duct and gallbladder during digestion. No dried food or grains. Raw beef mince, egg, spinach leaves and a spoonful of yoghurt for breakfast. Some partially cooked chicken and vegges for dinner. It helped more.
The final step was to feed him beef bones at least twice a week, in the dirt. I'm not joking - it was an accident the first time - it works! Raw beef bones fed to our dog on a patch of dirt. We allowed the bone to become covered in dirt throughout the eating process. Obviously healthy garden soil is preferable and avoid local environmental disasters.
It helped fix his digestive issues. He needs the beneficial microorganisms in the soil to help maintain gut health. Now he is the healthiest he's been since the accident! No more diarrhea!
Sometimes I think I forgot he was a dog and tried to keep him wrapped up in a blanket and fed on baby food. Certainly he needed that for a little while, but not in the long term.
All animals are different and even within breeds there is vast variation. Cats are different to dogs but both are evolved from meat eating species that lived in harsh environments without the "cleanliness" that humans surround ourselves with.
Perhaps our experience can give you a thought about how you might help heal your cat's digestive issues.