import scala.scalajs.js

abstract class A:
  type Props
  def apply(p: Props) = ()

object B extends A:
  case class Props()
  def apply(a: js.UndefOr[String]) = ()

Name clash between defined and inherited member:
def apply(p: A.this.Props): Unit in class A at line 7 and
def apply(a: scala.scalajs.js.UndefOr[String]): Unit in object B at line 12
have the same type after erasure.

Consider adding a @targetName annotation to one of the conflicting definitions
for disambiguation

import scala.scalajs.js

abstract class A:
  type Props
  def apply(p: Props) = ()

object B extends A:
  case class Props()
  def apply(a: String) = ()