How to switch back to ERC20 library solidity 0.8.18

The most recent version of the library requires ^0.8.20 as of now. The alternative is to install the previous v4. You can do it in Remix by suffixing your imports with "@v4.9.3" (the latest v4) as in:

import "@openzeppelin/contracts@v4.9.3/access/Ownable.sol";