I used to use Taste of the Wild to vary up the flavours, but a dog groomer ex told me that most brands bake their kibble into brown mush and then spray rendered fat on it to give it some semblance of taste/nutrition. She got me hooked on Bil-Jac which instead slow cooks their kibble with the bulk of it being proper chicken meat. It's wildly expensive ($65/30lbs locally) but there's something so Upton Sinclair about kibble in general. That's been the lesser evil I've found short of switching to a raw diet.
Kibble alone doesn't stimulate his appetite much. I mix in either peanut butter, pumpkin, part of a can of soft food, sweet potatoes, non-fat greek yoghurt, roasted root veggies, or peas just to change things up. He also gets a carrot or celery along with a dental treat every day, and I let him forage for a bit of grass on walks.
Apart from being slightly overweight out of hiking season, his fur/skin/teeth/GI health have all been pretty much ideal for 5 years.
Just a heads-up that introducing moisture to kibble creates an environment that's very conducive to bacteria so it shouldn't be left wet out of the fridge for long. People can sometimes find themselves in a bit of a trap where their dog has a bit of an upset stomach so they will only eat softened kibble or kibble with added stuff which introduces moisture, which then in turn creates an ideal environment for bacterial growth which then makes the dog have an upset stomach which then makes them a pickier eater and so on.
If your dog really doesn't like kibble then you could try alternating between kibble and some frozen raw meat/veg combination - note that kibble is nutritionally complete but stuff like chicken breast alone absolutely is not.
If you have the freezer space you might try buying up a variety of organ meats and combining it with cheap game (I'm guessing something like deer might be low cost in your region?) and then a mix of frozen vegetables, especially the higher protein stuff like peas while skipping out on the high carb vegetables like potato. You can either chop this stuff or blend it.
Aim for about 2/3rds meat/fish, 5-10% mixed organ meat, and make up the rest with non-starchy vegetables. If your dog likes bones then giving them bones with marrow inside is ideal too.
I'd go easy on the peanut butter because it's high fat and it's naturally high in aflatoxin - humans are well adapted to tolerating aflatoxin but dogs are less so. I'd use it for treats or for when you need to distract the dog when you're dealing with one that is tricky with grooming or medical stuff.
Sweet potato and root veggies are pretty high in carbs for dogs and I'd limit how much to give the dog.
If your dog is overweight and also a picky eater then that's sorta a problem that resolves itself - some dogs will scoff any food that is put in front of them but if you have a selective eater then generally speaking they tend to self-moderate and they'll eat enough that they are roughly within the right weight range. Lots of pet dogs are overweight and unless the vet is telling you that they are underweight then it's unlikely that your dog having a low appetite is cause for concern, unless it's a sudden change.
