Help understanding resolution settings

Hello all,

I’ve been playing with UE for a week and I love it !

I’m though a bit confused about how to manage project resolution and work with it.
Please note that I’m not into game development and intend to use UE for Filmmaking / Motion Graphics / Live Visuals, and I have a background as a 3D Motion Designer.

So, I actually don’t really understand where and how a project’s pixel resolution is managed… I know that you can seemingly setup the Level Editor resolution in Editor Preferences > Play > New Viewport Resolution but some things bug me out :

→ I tried to set it to a very low setting like 192*108 and I don’t see any effect neither in preview or game mode, everything is still finely displayed and detailed !

→ Working on a scene behaving fluidly displayed small in editor, when going fullscreen with F11, it starts to lag so it probably means UE tries to render it at my screen’s 2560*1440 native resolution

→ How can I display my scene, whether in preview or game mode, in a 1x1 “real pixel size” view ?

To put it in another words, how can I setup my scene at for example a size of 1920x1080 pixels, and keeping that resolution when going fullscreen ?
I know that when rendering out a movie I can specify desired resolution, but I would like to understand what is my displayed and scene resolution, be able to see it at real pixel size, and in case of live visuals, working at a specified resolution that I know has a good FPS on the machine that will play it.

Thank you in advance for your help, I looked up for it but it’s very unclear for me.