A basic ERC721 (NFT) implementation. Instantly runnable in remix.ethereum.org

MyNFT.sol

// SPDX-License-Identifier: MIT

pragma solidity >=0.7.0 <0.9.0;

import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/token/ERC721/ERC721.sol";
import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/utils/Counters.sol";
import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/access/AccessControl.sol";
import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/utils/Context.sol";

contract MyNFT is Context, AccessControl, ERC721 {
    using Counters for Counters.Counter;

    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");

    Counters.Counter private _tokenIdTracker;
    
    mapping (uint256 => uint256) private _tokenData;
    
    constructor() public ERC721("My NFT", "NFT") {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());

        _setupRole(MINTER_ROLE, _msgSender());
        
    }

    function mint(address to, uint256 tokenData) public virtual {
        require(hasRole(MINTER_ROLE, _msgSender()), "MyNFT: must have minter role to mint");

        _mint(to, _tokenIdTracker.current());
        _tokenData[_tokenIdTracker.current()] = tokenData;
        _tokenIdTracker.increment();
    }

    function tokenData(uint256 tokenId) public view returns (uint256) {
        require(_exists(tokenId), "MyNFT: URI query for nonexistent token");

        return _tokenData[tokenId];
    }
    
    function supportsInterface(bytes4 interfaceId) public view override(ERC721, AccessControl) returns (bool) {
        return super.supportsInterface(interfaceId);
    }
    
    function _baseURI() internal view override returns (string memory) {
        return "https://example.com/api/token/";
    }
}