No "REGISTER MODEL"
I do not see a REGISTER MODEL link at all in the actions page, does it still exist?
I might've found out why it doesn't show the Device Registration under Advanced Options. I already had set a fulfillment URL for a smart home, then changed my mind and wanted to do embedded (I suppose, just a guess).
However, I used the googlesamples-assistant-devicetool and added it that way, so now the Device Registration appears. Was a bit confusing and not straight forward, a GUI option would've been nicer ;) .. Hope this helps someone else.
Once you select a conversational or smart home action, it changes the console behavior for that action. In either of those cases Device Registration doesn't make sense so it's intended to keep it simple.
So then how would you go about switching? Should be an option on the actions console to switch, instead of digging through docs to find out other options.
Right now the best way would be to create a new project, which I recognize isn't ideal.