Dog becomes more reactive when walking near the house

As stated in the title, I have a reactive Chihuahua/Pomeranian mix who is around 6 years old now. He was fine as a puppy (carried him into stores briefly, had people visit the house with no issue) but then after all his vaccines and bringing him out for walks, he just explodes with reactivity and it’s so difficult to manage. He doesn’t respond to treats, at least when I last tried, at all. He gets totally fixated on the other dog or person.

I have been taking him to the park now a lot more consistently and he has gotten a little better. Just 5-10 minutes into the walk and he won’t bark at anyone and is relaxed.

I thought he had progressed, so I took him for a short walk around the house (in an estate with 30 other houses) and he just went crazy at a dog that was on the complete other side of a very wide road. If he was in the park he definitely would not have exploded like that.

Is this more of a territorial issue? The park is also more open and exposed, so he can see people/dogs more in advance before reacting.

Anyone have tips for training? It’s very difficult to get his attention during walks, but he is a smart dog and trainable, at home he loves doing tricks for treats. But on walks he finds it difficult to focus on me and does not respond to treats easily.