I think you're missing the point: it's incredibly hard to determine functional correctness of unreadable code.

So the first priority is getting the change to a readable state. I'm not talking about nits, I'm talking about minimizing the cognitive overhead to truly understand what the code is doing.

That being said, it is also easy to identify nits during this phase. In codebases that have collections of best practices, this often helps to ensure that the change is expressed in terms of a common vocabulary. Once this pass is done, the reviewer can usually better understand the intent of the changes.