Poor appetite is often a red flag, a sign that something may be medically wrong with the dog.
I would take him to the vet for a checkup and lab work, plus, whatever else your vet thinks is indicated. Once you diagnose what is wrong with him (or rule out), you can decide with the guidance of your vet what food would be best. Your dog is a senior, therefore vulnerable to all kinds of conditions that may be treatable. At the least, your vet should be able to advise you as how to keep him comfortable.
Do you want to eat when you don’t feel well? Didn’t think so.
PS: If your dog has had a full checkup within the last 6 months, just a call to the vet for advice may be helpful….
BTW those freeze dried liver treats and such may be high in fat and sodium, discuss with your vet.
