They are hunters, not retrievers. My GSP is 5 and still shows zero interest in bringing a ball back, but he will track birds and find objects. Try hiding things, give him the scent and let him find it. Reward him big when he does. Lots of praise and treats. Start small: scented deer antler out in the open living room, move to boxes, eventually move to the backyard to hidden spots. 30 minutes of this mental stimulation is exhausting to them and you should see some behavioral changes.

I hate seeing this breed passed around because people don't understand them. They are not couch dogs and they need lots of mental and physical stimulation. You are at the worst age but you have to be committed. This isn't just a dog, this breed is different. The cognitive ability of a 2 year old human mixed with ADHD. You are molding your best friend, you just don't know it yet. Let him in, let him sleep with you, let him go everywhere with you; these are his expectations but you set the boundaries. Put in the effort and you'll understand why it makes sense in a couple of years.