I can switch to 1080p resolution in my monitor ....
You don't see the real quality of 4K but you have a BIG ++++++ compare to a 1080p screenshot for exemple.
Every screenshot and trailers from games in development come from a 4K Pc.
Normaly i can give to people the option to choose their resolution for look the stream. I will see
You don't need to change the game or monitor settings, you can still play at 4k but just choose to downscale the broadcast quality to 1080p in OBS. Also those 4k screenshots look better on 1080p monitors because the picture is bigger than your screen and you can zoom in, when a 4k screenshot is fit to fill a 1080p monitor there is no difference because the monitor does not magically generate more pixels.