At my Wits End With 5mo Newfoundland Puppy

I recently got my own place and decided that I wanted someone to keep me company and so I got a Newfoundland puppy when he was 2 1/2 months old. He isn’t aggressive, loves people and other animals, potty trained quick and easy. He’s a great guy except for when he isn’t. It feels impossible, almost to the point of hopeless to exert energy. He’s getting better on walks but getting him to walk away from the house is impossible. He will just sit, lay, and stare at me if I try to leave the yard. I used to carry him a few blocks away, in which case he would bolt home. So I’ve been trying to play with him more except he doesn’t seem to care for any of his toys and after a minute of playing he stops seeing toys and only sees the hand holding the toy. This is becoming an issue because my hand isn’t for teething, especially because my newfs idea of puppy teeth is not the same as other dogs and it has sent me to an urgent care once (in one week he got me really good in the same spot 3 times and it got infected).

I’ve tried positive reinforcement with treats but he is not very food motivated and does not seem to care much when I get down to pet him and tell him how good he is doing. Not to mention, stuffing toys in his mouth when he bites just does not work! I’m at my wits end because I work 45-50hrs a week along with a singular college class and therefore I don’t always have time or energy to drive out to a dog/park just so he will listen a little easier. We go to parks Saturday and Sunday for a few hours and that tuckers him out tremendously but I just don’t have the time or energy for that every day of the week!I’m losing sleep as he gets bored throughout the day, but at the same time he does not want to do anything really to exert his energy.

Tldr: puppy is being a puppy except won’t play with toys and refuses to walk. No form of positive reinforcement works (treats, playing, telling him good job, etc) I walk him for 15-30mins a day 3-4 times a day but it just isn’t getting anywhere and he is bored of the toy chest filled with $300 of toys!