Anti-aliasing problem

**I`m trying to render a still in 3840 x 2160. No matter what I do, the AA turns out horrible in the rendered image. Jagged edges on a box. Everything is maxed at the the “engine scalabilty settings”. **

I`ve have looked for the answer out there and here, and the word used to be that you should render crazy large, and then scale it down. Is this still the workflow??? Is there something I have overlooked?
(Trying to upload images, but there are size limitations like those from the 90s!!!)