I received my Apple Watch Ultra a few hours ago and was bummed the Dexcom G6 app and complication didn't work on the Ultra (same thing happened with S7 last year). The app would say to check iPhone and the complication was just dashes. I set up Sugarmate so I could see my sugars (as you can see in the middle complication). I updated to iOS 16.1 beta 4 and the G6 app and complication started working.