Really? Who is biggest buyer of US debt?
Japan.
They don't have anywhere near as many treasuries as Japan. They are only a big buyer right now because there's a huge run-up in crypto.
Gurbacs commented that if Tether was a country, it would have been the top 30 holders of the Treasuries.
Also, Tether isn't a cryptocurrency. It's a pile of fiat currency represented by tokens on different cryptocurrencies. It's used to trade crypto on exchanges. They have hundreds of billions, so they park it in treasury notes.