You can certainly estimate the amound of USD held as StableCoin Collateral:

"The total market capitalization of USD-pegged stablecoins exceeds $220 billion, with over 99% backed by fiat currencies, predominantly the U.S. dollar." https://chatgpt.com/share/681e95fe-4308-8008-ab25-61be94a418...

RE: Nobody wants to own stablecoins, they want easier transactions. Agree but that does not mean anything. Stablecoins seem to be solving a problem, and there is not evidence of any traction by any currency other than USD.

So this phenomenon definitely runs counter to the conventional intellectual wisdom that USD is in decline.