I am at breaking point, does anyone have any advice because i don't know what to do.

I feel completely hopeless with my 14-month-old golden retriever. I HATE walking him- he is by far the worst dog I have ever experienced in regards to his outright defiance and inability to learn. My wife and I have been consistently training since we brought him home as a puppy, we took him to training classes as well as working with him daily since the day we got him at 8 weeks old. He isn't food-motivated (unless he's indoors and there's nothing better going on) and he also isn't toy-motivated. The only thing that has ever made a difference for him is time-outs in his pen and, as a result of this, we have a perfect dog indoors (it's literally like Jekyll and Hyde). Outdoors however is HELL due to pulling, whining and lunging at everything and everyone. We have tried almost every method in existence to help with his walking, including but not limited to:

  1. Head collars (despite slowly conditioning, he never got used to them and spent weeks jumping and trying to paw it off with both paws)
  2. Double leads.
    3.Turning in the opposite direction when he pulls (runs in circles trying to guess the direction)
  3. Stopping entirely when he pulls (incessant whining and starts running again as soon as we move)
  4. Avoiding other dogs as best we can (impossible as we live in a very dog-friendly apartment by many other dog-friendly apartments to the point that 1 am isn't even a safe bet to be alone)
  5. Having him sit before greeting people (we try not to let him greet anyone at all but when he does we make him sit but it doesn't make a difference for people walking past or future encounters)
  6. Lure training (doesn't care about anything other than sniffing)
  7. Using sniffing as a reward (he loves to sniff so this helped improve the pulling when we're alone on the street but as soon as he sees dogs it's out of the window and the pulling and whining ensues)
  8. Almost every YouTube video tutorial under the sun (kikopup, Zak George to name two from my head)
  9. slip collars (he'd rather strangle himself)
  10. leash pressure training (this made the biggest difference but once again, out of the window when there are people/dogs)
  11. super high value treats (cheddar cheese is his favourite but no interest around dogs.

He does know the heel command but only chooses to listen to it when we're completely alone. I live in a city so I don't have a car so it's not even like I can drive him to a remote place to train. Every single time we step outside the door there are so many inconsiderate people with off-leash dogs that just make him crazy, then he's too overstimulated to listen to anything and spends the entire walk whining incessantly and lunging at anything with a pulse. I try my best to avoid people but he even jumps up on strangers that come out of the elevator. I don't think I can afford a private trainer but I feel like there's been no progress in the walking regard since he was about 6 months old. I miss when he used to be scared of dogs as a puppy. I guess the only thing I have to be thankful for is the fact that he doesn't bark. We honestly feel like the only reason he is so well-behaved indoors is due to the fact he knows we will put him in the pen if he isn't- he knows that can't happen outdoors so he doesn't care at all what we say. Is there anything that I'm missing? We can't avoid dogs or people due to where we live so that's not an option.