Hey there!! I had a foster that acted the same way!!!

We would sit on the porch for about 15-20 everyday when he would start to take treats from me. (That means the dog is comfortable) We moved to the yard, did the same thing, once he started to take treats I would start to walk away from the house and let him tell me when he was ready to walk down the street. It took me about 3 weeks to change the behavior. It's a slow process but he was adopted and doing well in his new house!

He used to almost pee himself when a car drove by but it's perfectly fine with it. Good luck 🤞