Better type inference for multiple parameter lists in Dotty

What change in type inference brought better type inference for Option#fold in Dotty? For example

Starting dotty REPL...
scala> Option(5).fold(Left("err"))(Right(_))
val res0: Either[String, Int] = Right(5)

whilst in Scala 2.13.3 it errors

scala> Option(5).fold(Left("err"))(Right(_))
                                        ^
       error: type mismatch;
        found   : scala.util.Right[Nothing,Int]
        required: scala.util.Left[String,Nothing]

This seems to be related to multiple parameter lists such as Option#fold

fold[B](ifEmpty: => B)(f: A => B): B

which in Scala 2 work as follows

this behaviour or inference runs pretty deeply through the way that applications are type checked, and it is relied upon in APIs like foldLeft, which allow the constraints accumulated by considering the first argument list to allow you to omit types in the second argument list.

however it backfires in the above example because the "accumulated constraint" applied to second parameter list is Left[String,Nothing].