Did usdt always run on multiple chains? So years ago, it was only the on ETH chain?
There used to be only ETH chain if I am not wrong.
ETH chain is now expensive so avoid receiving using ETH chain. Tron chin is cheaper. You will need TRC10 or TRC20 address. Check with the gambling site which chain they have.
Is it ETH or TRON?
With your ledger you can have both. For ETH chain you will need ETH app to be installed and for Tron network you will need to have Tron installed.
Don't cross use any network. Like never send ETH chain USDT to TRON chain USDT or vice versa. There are nothing to make it complicated.