Updated July 2021.
- Create a Simulated Switch, it will the the master switch for the group. Alternatively, you may chose to designate one of the existing switches as the master
- In SmartThings mobile app select Automations, tap +, select Add SmartApp, 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! It will control all lights in the group.
Customer support service by UserEcho