Rendering to a portion of screen without cutting off anything that was visible during fullscreen

I want to render a camera’s rendering only to a part of game screen for which I change some numbers on that camera’s viewport. But, because of this I don’t see everything that I was able to see when it was full-screen(i.e. without changing anything in camera’s viewport). In the attachments below I see whole cube when rendered on full-screen but when I change the viewport to render on top left part of screen, part of the cube is not visible.

Is their a way I can render only to a portion of screen without cutting off anything that was visible during full screen ?

Try rendering the camera into a Render texture and then setting up a UICanvas with a Raw Image in it.
Place the Raw Image to cover the exact portion of the screen you want and put your Render Texture there.

This is now built in to unity. You can set what portion of the screen your camera renders to via the Viewport Rect setting on the camera component (under “Output”). I have some fixed UI that occupies the left ~40% of my screen, so my Viewport rect is {x: 0.4, y: 0, w: 0.6, h: 1}.