There are a lot of GOP-controller legislatures in the USA pushing through so-called “child protection” laws, but there’s a toll in the form of impacting people’s rights and data privacy. Most of these bills involve requiring adults to upload a copy of their photo ID.
Yes, it is one study. One study that performed a literature review and drew conclusions based on its findings.
As it is a review article, its conclusions are not experimental, but observational. It notes similarities between outcomes of different studies. However of particular note is that the conclusions that you are most interested in are all correlational. That is to say, the negative aspects of pornography were not observed to be directly related to the viewing of the pornography, but rather associated with the groups of people who tended to view pornography more. That does not mean that X causes Y, as it could be that a third variable Z is the thing that causes both.