the add-on was downloaded and I found it in the root folder of the game.Have you allowed time for the game to download? Open the Epic launcher and see if thee are any pending downloads.
Check for a folder "Products/elite-dangerous-odyssey-64" in your install folder
Yes, because otherwise it throws an authentication error and the client is closedDo you launch the game from the Epic launcher?
Just, for some reason, my launcher is not updated (completely reinstalled the game)Do you launch the game from the Epic launcher?
Rather, it is a Frontier synchronization problem. EGS and Steam only distribute the productIt sounds like an EGS problem, I would try contacting their support as well.