It's the Easy Access mode switch
"You can select this mode for easy access and easy loading of the vehicle.If the engine is stopped when this mode is on, the vehicle height is lowered automatically. The indicator light stops blinking, and comes on continuously to indicate that the shift is completed. The easy access mode is available when N or LO mode is selected"
It's on page 143 in this manual
https://www.manualowl.com/am/Lexus/2007-RX 350/Manual/6507?page=163