the extention installed fine but when I clicked "game" navigated to Fallout 76 and clicked "manage" Vortex expects Fallout76.exe which I dont have. Isn't this a vortex problem?
You misunderstand. The extension is not native to Vortex, it was created and is supported by a Nexusmods member.
The extension itself, not Vortex, needs to be updated to deal with the Gamepass version of Fallout76, which seems to be named differently from the original (Thanks Microsoft).
If you contact the developer of the extension and let them know your issue, I am certain they will provide an update. There is nothing anyone else (including Nexusmods staff and Vortex development) can do to help you.