Code doesn't compile when I paste into remix

[donaldnft]

When I paste the code into remix, it doesn't compile and gives this error:
ParserError: Source file requires different compiler version (current compiler is 0.8.0+commit.c7dfd78e.Emscripten.clang) - note that nightly builds are considered to be strictly less than the released version
--> @openzeppelin/contracts/access/Ownable.sol:4:1:
|
4 | pragma solidity ^0.8.20;
| ^^^^^^^^^^^^^^^^^^^^^^^^

When I put the compiler 0.8.20:

DeclarationError: Undeclared identifier.
--> contracts/LowGas.sol:99:7:
|
99 | _exists(_tokenId),
| ^^^^^^^