Simple small Savegas on-chain mint-myself Please let me know

Tell me about it.

・Using [remix]

・Compile (no errors)
・Deploy (no error)
・Mint (no error)

・Opensea(rinkeby) (error)

We couldn't find this contract.
Please ensure that this is a valid ERC721 or ERC1155 contract deployed
on Rinkeby and that you have already minted items on the contract.

Why is that?

What should I do?

My hope

・Smartcontract [simple]
・Smartcontract [small]
・Save gas
・Mint manually(myself) using [remix]

・Full on chain


wallet address
number (myself)

Please let me know.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC721, Ownable {
    constructor() ERC721("MyToken", "MTK") {}

    function _baseURI() internal view virtual override returns (string memory) {
        return "";

    function mint(address _to, uint256 _tokenId, string memory baseURI
    ) external onlyOwner() {}