[osama]

I’m very new to this, so this is not advice, it’s just me thinking out loud.
What I would try is to break down the issue into smaller, manageable sections. I’m assuming your dog likes to play on the playground behind the building. Use that.

At the door, before you leave, while the door is closed, do some engagement, like eye contact training. Then open the door and do the same. Then go a step outside on a short leash and do the same. If he starts reacting, go back inside immediately as a correction and start over. Take him back outside after he has calmed down and ask him to sit. If he reacts, go back inside. etc. Next time, do 2 steps, then 3.

imh you can’t fix this at once , you have to ease into it by taking baby steps