object Example {
    def exec(task: Runnable) = {
        task.run();
    }

    def main(args: Array[String]) = {
        exec(() => {
            println("Hello")
        })
    }
}

scala-2.13.3/bin/scalac Example.scala
javap -v -p Example\$.class

  public static final void $anonfun$main$1();
    descriptor: ()V
    flags: (0x1019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL, ACC_SYNTHETIC
    Code:
      stack=2, locals=0, args_size=0
         0: getstatic     #56                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
         3: ldc           #58                 // String Hello
         5: invokevirtual #62                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
         8: return
      LineNumberTable:
        line 8: 0

scala3-3.2.2/bin/scalac -d classes3 Example.scala
javap -v -p Example\$.class

  private final void main$$anonfun$1();
    descriptor: ()V
    flags: (0x1012) ACC_PRIVATE, ACC_FINAL, ACC_SYNTHETIC
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #60                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
         3: ldc           #62                 // String Hello
         5: invokevirtual #66                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
         8: return
      LineNumberTable:
        line 7: 0
        line 8: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       9     0  this   LExample$;