0xb6f9de95?0xb6f9de95 is the function selector for swapExactETHForTokensSupportingFeeOnTransferTokens(uint256,address[],address,uint256). ETH swap that tolerates fee-on-transfer tokens.
When a transaction's data begins with 0xb6f9de95, it is calling swapExactETHForTokensSupportingFeeOnTransferTokens. The selector is the first four bytes of the keccak-256 hash of the signature swapExactETHForTokensSupportingFeeOnTransferTokens(uint256,address[],address,uint256), which is how wallets and explorers work out which function a payload is for.