How do you configure which devices are activated for the Away and Stay modes?
I’m going to answer my own question because it took me way too long to figure this out and maybe it’ll help someone else:
Tap the Settings hamburger icon upper left.
Smart Home Monitor
Tap the Settings gear icon upper right (not “View sensors”)
TAP the Security (“Monitor your home for intrusions”) tile
(Yes, that tile has an on/off switch, but ignore it and tap the tile.)
You’ve got it, by default ST tracks all devices for all modes.
Alternatively you can build you own custom security system which are be armed via keypad or lock or other devices also by using modes or even Classic SHM integration. One key advantage here being you can track more types of devices than SHM offers.