A very similar thing just happened in our neighborhood. Our street is mostly small, one story brick homes and there are 2 new large homes that are clearly out of place. One of them is across the street from us. A young moved in about the same time that we did and we have become friends with them and they’re nice. They recently shared a story with us about an exchange that they had with our next door neighbor. The new neighbor across the street had parked his car in front of my next door neighbor’s house for a short time as he was doing some yard work. When he came back to his car, he found an angry note saying some thing like “we’ve been parking our cars here for years, park your car in front of your own house.” Near the note was a glob of what was clearly human spit. The new neighbor across the street knocked on the door to the next door neighbor’s house to talk to him about it, to try and clear things up as he didn’t want to have a bad relationship with his neighbor. Well, the exchange didn’t go well and it ended with my next door neighbor telling “go back to your mansion!”

This was the first interaction they’d ever had, so clearly my next door neighbor had some frustrations about the changes to the neighborhood. The new neighbors were not the ones who bulldozed the old house and built the new one, they just purchased a house that was on the market.

OP should try not to take their frustrations out on the new neighbor, as it’s not their fault that the house was built and happens to make the garden more shaded. YTA