Once all of the strawberries have been collected.

That will trigger the flag to unfold and fly out.

Once the Player touches the flag post

The level ends.

Create a new scene with Area2D as the root node

Rename it to CheckPoint and save the scene

Add an AnimatedSprite2D as a child

Create animations for the check point:

flag_fly (the file is called Flag Idle)

idle (the file is called No Flag) 

trigger (the file is called Flag Out)

Add a CollisionShape2D node

Use a RectangleShape2D shape

Fit it around the idle flag post.

Connect a script to the CheckPoint node