You probably never deposited any USDT, so your USDT wallet is inexistent. This happened to me, so I deposited like 5 USDT then withdrew everything.
edit: well, guess this was the case.

Thanks for the tip!
The wallet was already initialized with an initial deposit at the beginning of my Whale.io career (even if it hasn't been particularly successful so far

).
After the withdrawal via TRC-20 worked without any problems yesterday, I think it is actually due to the connection of SOL and BNB. Support told me yesterday that the information has already been passed on to the developers and is being analyzed internally.
However, the withdrawal itself went completely smoothly and the USDT are already in my wallet.