ADTs in Dotty are encoded as Enums instead of a sealed hierarchy.

adt-dotty.scala

// Note - these examples are not meant to show how the `Option` type is actually implemented

// Scala 2.13.x
sealed abstract class Option[+A]
case class Some[A](x: A) extends Option[A]
case object None extends Option[Nothing]

Some("test")
// has type Some[String]

// Dotty
enum Option[+A] {
  case Some(x: A) // implied `extends Option[A]` here
  case None // implied `extends Option[Nothing]` here since A is covariant
}
// Note: if A were contravariant, then `extends Option[Any]` would be implied for the `None` case

Option.Some("test")
// has type Option[String] because the apply method generated for `Some[A]` returns `Option[A]`

new Option.Some("test")
// has type Option.Some[String] because apply method wasn't used