When you form a mental model and then write code from that, thats a very lossy transformation. You can write comments and documentation to make it less lossy, but there will be information that is lost to an reviewer, who has to spend great effort to recreate it. If it is unknown how code is supposed to behave, then it becomes physically impossible to verify it for correctness.

This is less a matter of "mindset", but more a general problem of information.

You don't become a good editor, inspector, what have you, by having other people/machines write all the code for you. To become and, perhaps more relevant, to stay a good reviewer, you need to regularly write code from scratch to see how it works. On top of that, languages, frameworks and libraries change constantly and you need to write and execute and experiment with new code to see exactly how it behaves so that you can eventually review the code that uses these features. Good reviewers are not born good reviewers!