The squircle button behaves differently at different speeds. At higher speeds, it toggles the rear camera on/off. At low speeds it turns on multiple cameras.
A full windshield sunshade is unwieldy. Which means it doesn't get used.
I purchased 18"x26" sunshades. Easy to use every time. Big enough to protect the screen and squircle from direct sun. Small enough to store between the driver's seat and middle console.