Hello @SMSiegman and welcome to EBN
Sorry you're having trouble with Red Allergies are so common sadly. When trying new foods did you stay on that food for a few weeks/even months? It takes quite some time for the "old" food to get out of the system.
Did the vet suggest any other treatment for the Entropion? Eye drops can sometimes help and if surgery is to invasive it's possible to have a vet pluck the hairs if they cause issues. My Boeboe has had surgery, but before she had it her eyes would sometimes get like a blueish surface on them and she'd try to scratch them with her paws. Hers was pretty bad though
Do you use stainless steal bowls for food and water? Maybe try to add some coconut oil and/or plain greek yogurt to the food? Start off with just a little and after a few days normal dose is about 2 tbsp/day. It might help... but check for changes in stool in case he's sensitive to dairy.
They can be sensitive to so many things, it can be a chew toy, cleaning products, grass... basically anything. I'm not in America so I'm not good with the foods there, I know what you're feeding is great but if he's sensitive to it that's a problem I'm sure many more will come along with suggestions that knows the foods better.
Hugs to you and Red