Yes it is centralized. It is probably not backed by real assets neither. Since they refuse to do an audit we won't really be able to know the truth until it collapses. If you are going to hold your crypto for a long time tether is the worst choice out of them all the crypto out there.
If you keep your bitcoins in your own cold wallet no one can take it from you so don't use tether, problem solved.
the OP is already full member and he/she is just realising now that usdt is centralised? and that is true, i guess, we will never know the absolute truth regarding their pegged assets. if some will remember, way back in 2019, they admitted that usdt is not fully backed - just have a quick read of this
article . so up to you as a user or a holder, what will you believe now? usdt may be good for trading purposes but for long term holding, am not really up to it. just stick to btc if you don't know where to put your funds.