Code review is high-leverage when done well and counterproductive when done badly. The line is mostly about what you choose NOT to comment on.
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Substance first
Does the change do what it claims? Are tests covering the new behavior? Are there security or correctness bugs? Is the design fit for purpose? Everything else is below this.
Style: defer to tools
Formatters, linters, type checkers should be reviewers' allies. Don't bikeshed manually about quotes or import order — fix the tool config instead. Manual style comments age badly.
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What to skip
Personal preference without a clear reason. 'I would do X instead' when X is also fine. Rewrites disguised as reviews. Nitpicks on closing PRs.
Substance first; tools for style; skip preferences. Reviews should accelerate merging good code, not block on taste.