What about fish? I cannot recall the brand, but my darling Mr P luuuuuuurved fish. Especially the salmon.

ETA: I also gave him vanilla yogurt. He had food allergies and a sensitive tummy. The yogurt helped his tummy issue and eliminated the need for pricey pills. Stonyfield brand is organic, has probiotics, and he loved it.

Try sweet potato mixed with some protein.  Raw eggs.  I might coOk a little extra every night and make him a mix of dinner.  Just keep out the toxic people food for dog.  

Our senior pup has lost a few pounds, too. Best we can tell it's more from not absorbing nutrients than not eating.  He's picky but not super picky (had the same reaction as yours to peanut butter). A few of his favorites: the expensive Hill's Science Diet wet food. Of course he doesn't like the reasonably priced wet food.  Organ meats - he loves beef liver, heart, tongue. Also likes freeze dried liver treats. Hot dogs. Jerky, both dog treat jerky and the stuff I make at home in the dehydrator (low heat oven works, too).  Vanilla ice cream - soft serve from McDonalds is his favorite. We discovered this when the 3yo dropped her cone on the floor. Of course, this is probably not the best choice and more for calories than nutrition, but he really likes it.  

Our old, sick dog loved canned cat food.

I'm so sorry your pup isn't feeling well. My dogs are my babies and I know the stress they can bring. Do you try the rx canned dog food from the vet? It's a little expensive but try mixing it in with his..

SO tends to spoil our golden to eat (she can't graze because of our lab and sometimes she will just stare at you) so will mix anything in her food.. she likes greek yogurt! I would try broth too! 

Not sure if this has been mentioned but can you try mixing in some cheese/gravy/eggs/meats in with his dry kibble or wet food? 

GIve him lots of loves.

My dog loses her mind over those. 

I fed my aged shih-tzu/poodle boiled chicken and de-fatted gravy rubbed into her kibble. She was good with that for about a year before she refused food altogether. Having gone through the anxiety and stress that you're suffering, I wish that I could ((((HUG))))) you! ♥️

There are plenty of homemade dog food recipes out there. My pup has ear infection problems and we've been cyclying through them to find something that works. You said he loves pizza crust. How about whole wheat pasta? 

https://topdogtips.com/food-for-dogs-with-pancreatitis-recipe/