I feel this is a fairly common practice both in the console dev world through to the mobile dev world. You render your game at a lower resolution, but your UI remains crisp.
Lowering the game resolution gains you a performance boost since you need to render less. The result gets upscaled to full resolution basically for free. (Handled by the GPU). Then you render the game UI on top of that at full resolution.
I’ve done a lot of reading and the only way I’ve found to do this is to render the game camera to a 720p render texture and then also render the render texture as part of my UI.
However I am seeing a negative performance impact using this method. It seems like the overhead of rendering the 720p render texture as a full screen ui element/image robs me of any performance benifits I gained rendering at 720p in the first place.