Start Fortnite Windowed?

I want to be able to start Fortnite windowed before launching so I'm assuming there will be a setting in a local file somewhere that tells the game if it should launch fullscreen or windowed but I can't find it.

How do I launch the game in windowed mode?

Note: I do not want answers telling me to change a setting once the game has already launched.

Solution 1:

Mine opens in windowed mode by default when launching.

My setting are:

Windowed mode: Windowed

Display Res: 1680x1050 16:10

No changes have been made, this may be a change since the season 4 update as it never used to do this