There are two scenarios for TH not showing up in scene.
If you can’t find your TH device in the condition section .
To fix this, make sure the sensor of the TH device is plugged in correctly.
If it still does not show up after you pull out the sensor and plug it in again, then there could be some hardware related issue with it. Please contact your seller or manufacturer.
In case that TH device does not show up in action section.
This is normal, as TH device cannot be set as action device at the moment according to the app logic.