Why is the 'Estimated BTC Transacted' referring to just one of the multiple outputs? I recently started learning about bitcoins and came by this transaction. Here there are multiple outputs so if we consider one of them to be the change received by the sender then why is the 'Estimated BTC Transacted' only summing up to one of the output values? What happens to the rest of the outputs?
It's a best effort guess made by blockchain.com, has little relevance, is not particularly accurate, and should not be used for any meaningful analysis. It has no impact on the transaction, and is not part of the Bitcoin protocol.

It is somewhat accurate for very simple transactions, but breaks down for larger ones, and ones that utilize more recent anti-tracking approaches such as randomized outputs, sending change to an address of the same type as the other address being payed, etc.