In Configuration, if you go to Integrations and look at the Shelly one, you should see one or more Shelly devices, if you have added them. Click the one you want, then you’ll see a number of entities associated with that device. Click the entities link and it will take you to the Entities page of the portal. (actually the entities you see here are not visible via the normal Entities page route until they are enabled…) Click on the entity you want to enable and flip the switch in the resulting dialog. After a bit, this entity will now be visible the normal way and useable in a template for a detached switch.
I have seen though (why I was searching and found your question this morning) that sometimes these entities become disabled, not sure why - I had to re-enable mine for the detached switch template to start working again.
