How to switch off iPhone XR?

See the following from Restart your iPhone - Apple Support

How to restart your iPhone X, 11, or 12

1. Press and hold either volume button and the side button until the power off slider appears.
2. 
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4. Drag the slider, then wait 30 seconds for your device to turn off.
5. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.

How to turn off and restart iPhone 11, XS, XR, and X

Press and hold the Side button and one of the Volume buttons until the power off screen appears.

Drag the slider to the right to turn off your device.

Press and hold the Side button to power it back on and complete the restart.