0x49404b7c?0x49404b7c is the function selector for unwrapWETH9(uint256,address). Unwraps WETH back into ETH.
When a transaction's data begins with 0x49404b7c, it is calling unwrapWETH9. The selector is the first four bytes of the keccak-256 hash of the signature unwrapWETH9(uint256,address), which is how wallets and explorers work out which function a payload is for.