Considering how poor soundproofing standards in America are, and how inconsiderate the average American is, apartments are not a consideration for anyone who can half afford a SFH.

This is not inherent to apartment buildings and is probably mostly an issue with the smaller wooden ones. I live in a 30 level building and haven’t heard a single sound from any neighbours. Turned my music up to what I used to in a house, went in to the hallway and could hardly hear a single thing from directly outside my door.

Probably the easiest way to find out before buying is to just stand in the lobby and ask the next person who walks past what they think.

Where do you find properly built apartment buildings with a soundproofing barrier in the underfloor and brick party walls?

My in-laws lived in a mid-height (4 floors) concrete-and-brick building that went up under Salazar. An equivalent building in the US would be built in wood and sheetrock pretty much everywhere. Even 5000 square foot doctors' palaces that go for half a million dollars are stick-and-cardboard. Solid construction you'd only find in highrises in urban centers, and even then it's not guaranteed that the walls aren't made out of cardboard.

You see these sprawling neighbourhoods of SFH's with 1.50 m separation between buildings and very much the whole lot paved over. Everywhere else there would be mid-rise multifamily buildings, but the American insists on an SFH, because soundproofing.

To be honest, I'm not sure what the appeal of mid height buildings are. They have all of the downsides of an apartment with none of the upsides of a high rise like better quality construction and better location.

To find out what the quality of a building is you are best off just asking people who live there what they think. Apparently you can also request that strata give you information like owner complaints which may bring up noise disputes.

The point of mid-height buildings is that you can line a road with it and get sufficient density so that all the urban amenities (parks, playgrounds &c) are within 15 minutes of walking. That was Salazar's explicit goal when he built the post-war Lisbon neighbourhoods - church and primary school were the focal points and had to be within walking distance. His architects did an admirable job.

But what's the appeal of a high-rise? It requires too much space around it, it's not made for the human scale.

Depends what the definition of high rise is I guess. I live in a 30 level building that I consider pretty high and it sits on the entire space of the block it is on with only walk ways between it and the next building. I'm more talking about these 4 level apartment buildings which seem pointless to me.