How to get the Shelly Update entities enabled for a Shelly Plug S?

I have multiple shelly plug s. They work flawless. I would love to update the firmware from Home Assistant directly instead of WebUI or ReST API. I can see that there is an update-entity (also mentioned by the docs), but it is always disabled (message: Not available). This is the case for all my shelly’s (all pretty up2date). The docs does not mention anything how to get the entity enabled.

Is there a trick to get the update entities working for a shelly plug s?