Hello @mudtonk @MrMelch please try the following:
Navigate to
C:\Users\YOUR_USER_NAME\AppData\Local\UnrealEditorFortnite\Saved\Config\WindowsEditor\EditorPerProjectUserSettings.ini
on your computer and open the file. Then, search for
bStartupWithLastProject
It should be set to =True so set it to be =False
Reopen your UEFN and hopefully it works!