It depends strongly on the city, and became more pronounced since covid.
replySeattle is the worst. They call it the "seattle freeze." The San Francisco Bay Area became almost as bad in covid.
The south is still friendly. Austin is incredibly friendly with strangers. Miami has strong stranger vibe. NYC is still alive, too.
It may also depend on where you're from. I'm British, have travelled around the US, and never had problem engaging in chit chat with all sorts of people, big cities or not. But there's a strong disarming undercurrent of "oh wow, you're from England" through the whole experience that I expect most Americans never experience, at least within their own country.
replyTourist areas of large cities are like this. LinkedIn connections are like this. Other than that, people are delighted when you speak to them for the most part.
replyIf nothing else, the nerves and flashbulb memories overwrite old nerves and flashbulb memories.