0x813500fc?0x813500fc is the function selector for setApprovalForAll(address,bool,address). Operator approval variant with an explicit owner.
When a transaction's data begins with 0x813500fc, it is calling setApprovalForAll. The selector is the first four bytes of the keccak-256 hash of the signature setApprovalForAll(address,bool,address), which is how wallets and explorers work out which function a payload is for.