unless Tether has a video camera that livestreams a bank vault where every bank note has been seen and counted. and it shows the auditors doing an actual count that can be proven. where watching the livestream shows money-in money-out.
unless the above, you cant fully verify reserves
Such task is nothing important for them and they always give excuse about "privacy".
Even such thing exist, I can counter your argument by saying if the bank notes are fake, so it's useless even the auditors count it.
so the risk of Tether collapsing because of a lack of reserves will always be there, and this is true for all stable coins and centralized projects, there are simply too many examples of this through history, which is what motivated Satoshi on the first place to create bitcoin as an alternative.
Yeah there have been many stablecoins lost it's peg, this is the full list
https://chainsec.io/failed-stablecoins/