I am having this problem as well with my Apple Watch and app version 6.4.5. Shows the "You can add items from the 1Password app on your phone. Requires Pro Features" but there is not a button in the app to add to Apple Watch. I can follow your instructions above to send the diagnostics if that's the best route from here.
Never mind, I figured out it only works with Primary vault and not Personal vault (1Password Teams/family)
That's correct. Sorry for the confusion there! We're working hard on a new version with support for all vault types. I can't say when it will be finished, but we're anxious to get it out there so all of us can enjoy it — once it's ready.