I am interesed in he ES novels. But are they regarded as canon or "fan fiction"? Do anyone know?

The novels are not in your Elder Scrolls game, they are not part of your Elder Scrolls game and they are not the work of Bethesda.

Those are all the facts you need to know.

The novels introduce several things to the story that Skyrim builds on further, such as the destruction of much of Vvardenfell, and the invasion of southern Morrowind, the Mede dynasty of Emperors, and other things.

Pete Hines: "https://twitter.com/dcdeacon/status/21951830233710592".