Maybe half of those 14 views also want to know the answer or didn't have advice to give.
Innova Evo red meat is very high in protein. So Peanut is probably eating just enough to satisfy him. Is he neutered? Neutered or spayed pets tend to gain weight, mine eat like piggies.
IMO, I think an only Yorkie doesn't eat as much as he would if there were one or two or more.
If his vet says he looks good & he checks out ok, I wouldn't add stuff to his food to entice him to eat. He might start to not eat unless you add something, these guys are smart ya know! Plus you don't want to go overboard on the protein, these guys are small & 20something% of daily protein is suggested. Sorry, I don't remember the exact #, but Innoa red meat is 40+%. It's very high.