Thanks for all the answers!
Then which chain should I use to store USDT?
If you want to hold it long term(I don't know why, but each person has their own reasons), then you might as well do it on blockchains that have a decent reputation and that have been live for a while now: Ethereum and/or Solana.
If you want to hold BTC, then hold BTC. If it's on a different blockchain other than Bitcoin, then it's WBTC(wrapped BTC).