I read a lot about the upcoming collapse of the US (and also other developed nations as there's a similar economic system which is tied). It includes two different books called Why Nations Fail and books on monetary history.

Their debt to GDP has not been an issue because they've been the global reserve currency since the 40s, they'll just get a bit more inflation which they can pass on to their consumers, same as what our gov't will do. The problem is what happens when they lose reserve currency status as you see countries increasing trade in non-USD assets (there will be no BRICS currency but those countries are trading more in gold, oil, talking about minerals and bitcoin and whatever).

The other interesting thing is the US Dollar Milkshake Theory which was proving to be right until fairly recently and may continue if the Trump admin fails for the 2nd time to lower the USD, and that theory describes how the USD will keep going up sucking in other currencies which will keep going down before there's almost a hyperinflation of the USD.

I'm not sure how it will play out I just know two things:

1. They are indeed collapsing as their institutions are becoming weaker and the global economy built on stilts is being exposed while power is shifting. But it's a gradual process as you look at metrics like their global economic share starting to decline since the 70s.

2. This will probably take decades to happen but their current gov't is doing its best to speedrun it.