The correct option is Pull requests where that user has been invited to review.

When you search pull requests using the review requested qualifier with a specific username, GitHub returns pull requests where that person has been requested as a reviewer. It focuses on pending review requests and does not require that the person has taken any review action yet.

Pull requests that were opened by that user is incorrect because that is matched by the author qualifier which filters by who created the pull request rather than who has been asked to review it.

Pull requests where that user has submitted a review or an approval is incorrect because those results come from the reviewed by or approved by qualifiers which indicate the user has already acted rather than simply being requested.

Pull requests assigned to that user is incorrect because that is covered by the assignee qualifier which is about task ownership rather than review requests.

Full AWS Practitioner Certification Question