Updated February 2021.
- Create a Simulated Switch, it will the the master switch for the group. Alternatively, if you don't want to create a virtual switch, you may chose to designate one of the devices in the group as the master switch.
- In SmartThings mobile app open left hamburger menu, select SmartApps, select Smart Lighting, Create a new Lighting Automation
- Select all lights that you want to control as a group under "Which devices do you want to control?"
- Select "Mirror Behaviour" under "What do you want to do?"
- Select the master switch from the first step under "Mirror which switch"
Now, the master switch can be added as a Tile!
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