The ratings are in the report linked by OP. Vast majority A-2 or better (S&P).

ryan_lane · on Aug 12, 2021

And many are self-determined and put into (S&P) terms, because they aren't otherwise rated.

Tether has outright lied numerous times in the past, and have been caught doing so. Why would you believe their attestation when they won't allow audits?

kwere · on Aug 12, 2021

Because trust Is the base of a society. Why wouldnt You trust a bunch of whitcollar excon? Have Faith!