When opening a Fortnite session using the “Launch Session” button in UEFN on a 1440p (or I would assume higher) monitor, the game will launch in a 1920x1080 window in Windowed mode.
After it is launched, it WILL NOT let you change it to any resolution higher than this. This gets kind of annoying, especially because if I want to play Fortnite for a bit after doing some development, I have to relaunch the game so it can open in Fullscreen or Windowed (Borderless) Fullscreen.
Here’s a screenshot of the settings window (UNCHANGED).
No matter what I try to change Window Mode to, it will stay in this window. See this example where I set it to Fullscreen and then hit Apply:
I do like how it opens in a window, since I like being able to have it not fullscreen while editing, but I really wish it would give us the option, maybe in a dropdown aside “Launch Session”