I wish 4K (3840x2160) monitors would show a 1080p signal at a completely sharp 1-input-pixel-becomes-4-output-pixels.

They all seem to get some blurry scaler chip involved even when the numbers divide cleanly.

You can actually choose that as option in the AMD or Nvidia control.

You want to select the scaling mode Nearest Neighbor instead of Bilinear.

I think you may be imagining that, at least for AMD. Where is the option located?

You are indeed right, this was once in the Catalyst center, but the radeon controls never got the feature: https://community.amd.com/thread/195561