How can we enable downscaling without a RenderTexture?

Lots of games have an option to increase the internal camera resolution above the display resolution (downscaling).

Currently in HDRP there is no way to do this, even with Dynamic Resolution (the maximum we can set is 100%).

I tried using a RenderTexture and then rendering it with a Canvas but the performance impact is quite a lot compared to just changing the resolution in the Game view.

Is this simply not possible or did I miss something?