So if person A has USDT on Ethereum and person B on Tron, basically those are 2 different tokens a d person A cannot send Tether to person B?
Yep, correct. Since both blockchains are isolated on its own network, inter-transaction of USDT are not possible.
Another scenario is
A send USDT on BEP20 chain to B, but B is expecting to receive it on the ERC20 chain. Due to the nature of the underlying technicalities, the transaction will be accepted but the transaction is only happened on the BEP20 chain, not on ERC20, thus B did not receive the token.
Ufff wow, didn't expect it would be so complicated
Yes, it is. If you don't know how exactly sending crypto work is, you will end up lossing them upon sending, depositing or withdrawing on exchanges or wallets, though it might have some solution to recover it, but its too technical.
It is not very complicated because USDT is a stablecoin which are present in a lot of blockchains now. And if you want to transact with USDT, make sure you are in the right network. Otherwise, your funds are considered lost.
If you will read this article -
https://www.coindesk.com/markets/2020/03/20/tether-stablecoin-launches-on-its-seventh-blockchain/, this article is almost 2 years old already. And at that time, USDT was already present in about 7 chains already - Algorand, EOS, Ethereum, Liquid Network, Omni, Tron and BCH. And I guess, today, there is SOL, MATIC in addition to that and other new networks. If you happen to check the exchanges, it will show you what network you want to use.