Same here. Something is definitely off in 4.23. We also moved from 4.22 to 4.23 and suddenly the game is on both of my screens.
In 4.23 I added this to my Level BP but it doesn’t solve the problem:
If I start PIE it works just fine and also rewrites my GameUserSetting.ini
In Standalone it doesn’t rewrite my GameUserSettings.ini but has the correct resolution
With right click on exe an LaunchGame - closes test to packed game - something is resetting my GameUserSettings to 2880x1080 and displays that resolution. This doesn’t happen if the second screen is unpluged. But either way this BP code gets ignored, same with setRes. Even if I copy the right GameUserSettings in my config folder not in saved/config.
It’s probably a new setting / default value we are missing here.