My pup started to not eat his dry food too and I tried a bunch of the same things as you. Idk how many bags of dog food I have from when he wouldn't eat them but all is well now since I have this he eats his food pretty much right away now. I think they have different flavors but my pup has always been partial to beef so I got that one. Might help and it's only a few bucks. Also he goes for the food and sometimes eats it all even if I don't put the "seasonings" (lol) on which is great.
Mine is a fan of these beef liver sprinkles!