I see no way to select it in FCPx. I have it connected via sidecar.
I CAN do it in Resolve as a clean feed, but not an external device like a black magic Sdi card.
I can turn reference mode on and off on the iPad while still connected to sidecar.
I don’t think the mac controls that at all. I think it’s just like one of the reference modes on the XDR but there is no documentation.