That makes no sense whatsoever. If I can buy everything in BTC that demonstrates that something happened very wrong that makes USD untenable for basic, or any kind of, transaction.

That's a very American-centric view. The fact that Amazon UK accepts orders in euros doesn't mean that the pound is untenable for any transaction. Similarly, Amazon accepting Bitcoin (thus meaning you can buy almost everything with BTC) doesn't make the dollar obsolete.

Please. Normal Forex is not the same as a deflationary crypto currency being trusted enough for normal transactions. If in the future I indeed can buy everything with cryptocurrency then I stand by my feeling that something must’ve gone quite wrong.

Why is it not the same? It'll be fine.

Yeah , I do think there are those who believe in a collapse of normal economic systems but the reality is that things would probably just transition to it.