In some cases, Ubisoft has sold multiple versions of a game in your geographic region. After you have performed Ubisoft account linking, GeForce NOW should automatically select supported versions.
For games purchased on the Epic games store, you must link your Epic Games and Ubisoft Accounts to properly work with Ubisoft library sync. Please read this support article from Ubisoft on how to link Epic Games and Ubisoft Accounts.
Ubisoft account linking does NOT work with Ubisoft games purchased from Steam.