Give him time. It can take an adult dog at least a month to adjust to a new home. Maybe he would prefer a little wet/canned food mixed with his kibble. I would add a little water to it.
Don’t hand feed. Feed twice a day, offer the meal if he doesn’t eat within 10 minutes pick up the dish and cover it, store in the fridg and offer it again at the next mealtime. Don’t leave food down all day. Just fresh water.
How do his teeth look? Any discomfort would affect his appetite.
As long as he is drinking water I would not be concerned unless he eats no solid food times 72 hours, at that point I would consult a vet (in real life not on the internet). You should find a vet near home to take him for annual checkups.
If he continues to have difficulty adjusting it wouldn’t hurt to have your vet look him over.
Dogs can suffer from anxiety and depression just like people do. He may be grieving his former home.
Patience.
In the meantime take him for walks, see if you can interest him in a game of fetch. Just hang out with him, let him get comfortable in his new home. Dogs love routine so walk him at the same times every day, meals at the same times (8a and 5p) for example.
Offer bathroom breaks frequently, especially first thing in the morning and bedtime.
You will see a very different dog in about a month or two .
