Check out this neat post about Google manual reviewers from Neil Patel on how to see if you have had any manual reviewers to your site?
Sounds like they either do spot checks or manual verifications at time to see if their algorithm is ranking quality posts properly for the right spots.
What if you don’t see any hits? You’re okay, they probably do only a small percentage of checks manually.
What about if you see some manual hits by Google? Then just make sure you’re up to date with your content, that its IS good in terms of providing your reader quality, and also try to check all the boxes of what Google wants.