I fixed the problem with the "Approve" function call. I created a hash from the signature "Transfer(address,address,uint256)", which is then used in the topics array as the first element. With this I could test it and don't get the "Approve" calls anymore.
But I guess there is still a remaining bug. If I sum all transaction from 20th November, the sum is only 2.5 billion USDT. But coinmarketcap says it was 72 billion USDT. So maybe I missed another function call?
BTW, pretty high volume. I did a sort for the highest transactions, and there were 2 with 111 million USDT, just yesterday: