What I understand is that desert and beach sand tends to be old/heavily weathered sand that is too fine with rounded edges. And is physically weak. Sea sand also tends to have chlorides which causes problems.

The foundation of the house I'm living in was probably made with beach sand (1908 construction). One wall that gets wet frequently is turning to dust.

Is it really a problem a 100 year old structure of non historical significance is showing signs of age?

Until very recently (2 weeks) ago everywhere I had lived was at least 150 years old - so that seems a very odd concept to me.

Flip-side of that is the timbers are all old growth redwood. If you ever poke at the stuff after 100 years as long as it didn't get wet it's fine. 50-50 chance whoever buys this place will replace the foundation. And hopefully with proper concrete. Do that and the building will last into the next century.

Yes.

Or what is your point? That we use too fine grained sand to build our cities and then let future generations deal whith grumbling skyscrapers?

The point is supposedly that providing housing for the current exploding population is more important/urgent than their great-grandchildren having to tear down and rebuild their houses in 100 years.

Well, if the foundation of the house where you live is crumbling, I'm sure you'll admit it's not good.

The video notes that desert sand is too fine to be used in construction.

There is a beach in south Sweden which was mined for sand, I think it was for biosand filters for water purification. The said they exported sand to Saudi from there. I presume different sands have different properties.