Addendum:
What food did your veterinarian recommend? It doesn’t sound like you are overfeeding him.
You can presoak the kibble in water or plain homemade (nothing added, boiled chicken water)broth. I would say no snacks, except maybe a raw carrot here and there.
How about: https://www.chewy.com/natural-balance-fat-dogs-chicken/dp/46804 Only 250 calories per cup!
I hope these articles help: https://www.mspca.org/pet_resources/the-skinny-on-pet-diets/
and https://www.mspca.org/angell_services/choosing-the-right-diet-for-your-pet/
I would increase the walks, even if they are slow and leisurely.
PS: Brush his teeth once a day, they love chicken flavored toothpaste.
