I’m reluctant to potentially hijack this thread, but I seem to be having a similar issue, albeit in a different context.
The (newly cloned) iPhone 12 I am using as a remote to control other endpoints - successfully control - doesn’t itself show up as an endpoint in the Audio settings pane. Other endpoints are visible, including another iPhone, but I can’t even see the very iPhone I am using as an endpoint to configure. So I can’t set it as a private zone - it’s not visible to do so.
Will try reinstalling Roon app, but this has happened along with some of the first issues in connecting to Roon core from this phone or any other I’ve experienced on my network. No issues with controlling other endpoints, as I say, so not sure if other networking details required here.