Understandingdefinitionanddesugaringof"Option"inScala3book

I'm starting a Scala role in a few weeks yet I haven't written any Scala before (yes, my future employers know this), although I've written a lot of C# and Haskell. Anyway I was skimming through the Scala 3 book, and found this example:

enum Option[+T]:
  case Some(x: T)
  case None

Which apparently dusugars into:

enum Option[+T]:
  case Some(x: T) extends Option[T]
  case None       extends Option[Nothing]

My two questions are:

1. How exactly does the mechanism of this desugaring work? In particular why does Some by default extend Option[T] whereas None extends Option[Nothing]?
2. This seems like a strange way to define Option. I would define it like this:

enum Option[+T]:
  case Some(x: T) extends Option[T]
  case None       extends Option[T]

Indeed with None extending Option[None] wouldn't this fail?

Option[string] x = None;

As Option[T] is covariant in T and None is not a subtype of string?

I'm missing something quite fundamental here I'm sure.