Passthrough is a feature for Oculus Quest that allows you to temporarily step outside of VR to see a real-time view of the world around you. Passthrough will automatically trigger anytime you step outside of your defined playspace within your Guardian.
If you enable the Passthrough shortcut option in the Experiments section of your settings, you'll be able to manually enter Passthrough by tapping the side of your headset twice. Double-tap the side of your headset again to return to VR.
Please note, there is no physical button used to enter Passthrough.