OpenZeppelin's (openzeppelin-contracts) change the security files into the "utils" folder, so for the Lesson12's contracts
import {ReentrancyGuard} from "@openzeppelin/contracts/security/ReentrancyGuard.sol";
should change to
import {ReentrancyGuard} from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
then you can successfully import the ReentrancyGuard.
OpenZeppelin's (openzeppelin-contracts) change the security files into the "utils" folder, so for the Lesson12's contracts
then you can successfully import the ReentrancyGuard.