Sloppy U.S. construction is your issue, not density. Walls can be built to be sound proof.

You must've lived in some really badly built stuff (not surprised, US buildings are usually on the worse side of construction quality).

I'm living in a modern German apartment building with about 24 parties. The only thing I hear are when the children in adjacent apartments go full blast at it, screaming like they're tortured (probably having to eat their cauliflower). Other than that I only heard my neighbor once, apparently having the sex of their lives (it was super quiet in the middle of the night). I chuckled and went back to sleep.

The walls between row houses should be even thicker if build properly, you shouldn't really hear anything except extremely loud bass. And depending on the quality there even are building techniques to muffle those (I think by leaving some air gap inside the wall).

Houses in the US have thin walls. Nothing prevents something slightly denser without it being row houses, and something mixed use without it having loud and obnoxious night life.

Your buildings in America are built cheap af lmao. You dont even know you can live without hearing your neighbors next door 🤣