All-wheel drive lock mode can be used when a large amount of drive power needs to be applied to all the wheels, such as when the vehicle gets stuck in mud and you need to free it.
Press the switch.
The torque of the engine is distributed to the rear wheels to the maximum extent possible in accordance with driving conditions.
Pressing the switch again cancels all-wheel drive lock mode and returns the dynamic torque control awd system to normal mode.

All-wheel drive lock mode can be operated when
All-wheel drive lock mode
Things you should know
Driving assist systemsCustomization
Your vehicle includes a variety of electronic features that can be
personalized to your preferences. The settings of these features
can be changed by the meter control switches, on the audio system
screen or at your toyota dealer.
Customizing vehicle features (audio system screen)
Audio system ...