If I was doing a proper review of a PR that big and making sure you understand how everything works that would easily take multiple days and generate 10s-100s of comments.

In reality I would flat out refuse to review it. Even 1k is very large without being broken down.

The only time I see PRs that big at work are cleanups (E.g. deleting whole directories), automated linting changes across the whole codebase and large structural refactors (E.g. changing directory structure).