Hello! 
The issue here is that WeMod does not currently have access to the Wintermute DLC on Epic Games, as it has not yet been released there.
Wintermute - which is the game’s “Story Mode” - was originally included as part of the base game in earlier versions. However, the developers have since separated it into its own standalone DLC. If you purchased the game before this change, that’s likely why you still have access to it.
Unfortunately, until the standalone Wintermute DLC is officially released on Epic, WeMod won’t be able to support it on that platform.