How do you set up crisp textures?

I downloaded a 4k earth texture and put it on a sphere but when the camera gets close it looks blurry and not very high resolution.

After downloading and bringing it into UE, you can doubleclick on the texture, and the first thing you should check, is, if it is actually displayed at the full resolution, or if it´s somehow scaled down.

If there is a difference between “Imported” and Max ingame, then expand the arrow in the compression settings to get access to that “Maximum Texture Size” slider, and set it to 4k in your case.