You can now create huge renders in Unreal Engine using a tool called "Movie Render Queue".
It works by adding a new level sequence and adjusting the output:
Select the output to play to render to one frame by using the "custom by playback range" function
Override the default anti-aliasing settings which gives that low-quality "step" effect to your image - and increase the temporal sample count (how many times the image will be rendered stacked on top of the other) to give a smooth final image
Select the desired image resolution
Set the camera compensation to manual exposure
Use the high-resolution tile count to have a tile resolution of less than 4K
Watch the video to find out how to render ultra mega-high resolution renders in Unreal Engine: