i belive i know what you mean, many games have for example 50% resolution scale, so while it use bigger resolution, render is done in lower resolution.
still did not try make it myself, but i belive it would need to make default render into Texture(size you want) and then scale this texture into screen.
there are some topics on HUB, you would need look, like for example: Render resolution and scaling? or Render to texture solution - #11 by thetoucher but any of this require you to use some tricks.
also belive @RiccardoBlb new Pipeline will allow something like this without “tricks”. But need wait.