The black tacky plastic piece on the driver's door represents a linear graph of sales by units.

 

It’s not a real vent - it’s just a styling insert.
Lexus uses it to break up the side profile because the GA‑K platform has a tall, flat body side and would look even more slab‑sided without some kind of visual interruption.
Painting it black is part of Toyota/Lexus’ current “contrast accent” design language.
It doesn’t do anything functionally, but it helps them visually lower the car and add some tension to the shape.