How do I set responsive background from image?

I have a viewport of the game set to 1080 x 1920 (9:16). I want to change the size of the viewport to be responsive to fill the black background of the area that is outside of the set viewport.

I tried to create something similar to this tutorial: youtube.com/watch but no luck.

Does anyone have an idea how to solve this issue?

change the fullscreen mode from letterbox to scale inner or outer.