Not many mixers support USDT since they can be frozen. Tornado Cash got their entire USDT and USDC stack frozen when their addresses were added to the USA sanctioned list, too risky for a privacy oriented service which is much disliked by government agencies worldwide.
Just exchange for USDT on an instant exchanger if you want good USDT. You're receiving clean crypto from the mixer anyway so it's not like it's gonna get flagged or anything.
