So afaik, the DNP can take many different forms. The first, and most used, is as you said. Only the artist can post their work (sometimes with specific instructions that let others post as long as they follow them).
Another that some people on both sides if I’ve been keeping up with this, is to not allow posts except from the artist, and to delete all current works on the site. This is because they don’t want their art or works showcased on a site that is against their beliefs (wether that be for “anti-censorship” or “anti-nazi”)
There are a multitude of other different kinds of DNP, but those are the most prevalent through this whole mess that I’ve seen. Hope that helps