How to assign iPhone "Shortcut" to record video? iPhone XR large button on right: double-tap brings up Apple Pay.  I would like to be able to remap the double-tap to record videos and not miss recording key events tapping through the menus to invoke video recording.
The goal is to pull the device from the pocket and start recording with a single command (preferably without looking at the phone, so as to keep an eye on the event).
How is this possible, if not, what is the next best option?
You cannot change the action of a double-press of the side button.
You can configure back tap accessibility feature:

Create a shortcut to Take Video with the Camera app.
Configure back tap (Settings → Accessibility → Touch) to run the shortcut you created.