0x4f1ef286?0x4f1ef286 is the function selector for upgradeToAndCall(address,bytes). Replaces the contract logic and immediately calls into it.
When a transaction's data begins with 0x4f1ef286, it is calling upgradeToAndCall. The selector is the first four bytes of the keccak-256 hash of the signature upgradeToAndCall(address,bytes), which is how wallets and explorers work out which function a payload is for.