What are the four small LEDs for on the bottom of the controller?
They are controller mode indicators:
A. LED 1 blinking: D-input mode
B. LED 2 blinking: X-input mode (Xbox 360 mode)
C. LED 3 blinking: macOS mode
D. LED Rotating: Switch mode or pairing mode
E. Solid LED: connection is successful
*It also indicates the player mode when connected to Switch.