I had a similar issue with a cat except 70% or his poops were also liquid.
After maybe 2 years of trying stuff and vet appointments, We got a non chicken based dry food (pretty sure he has a sensitivity to it) occasional scoop of pumpkin and goats milk to keep his gut in balance. All available at the pet store, or Amazon.
Been good for like 3 years now on the schedule.
Oh that’s nice. We never had a vet tell us that. We ran into a random article on the internet and figured we outta at least give it a shot.