Beat together butter and 2/3 cup sugar until combined.
Add in flour and blend well.
Add in the vanilla.
Roll into cookie doughs - about 2 tbsp per cookie dough. Place cookie doughs on air fryer parchment paper.
Press down on the balls to flatten with the bottom of a cup. Add rainbow sprinkles. Then press down with the bottom of the cook and lightly press down again just so they stick. (Note: just sprinkling on the rainbow sprinkles on the cookies would not make them stick very well. So I added some sprinkles on a plate and gently pressed the tops of the cookies into the sprinkles. Then flattened the cookies more with the top bottom of the cup.)
Place in the air fryer basket. Air fry at 320 °F for 7-8 minutes, or until browned and cooked to your liking.
Let the cookies cool slightly outside of the air fryer basket before enjoying (to help them set).