MaryB But those aren't in either Insider ring, right? The logic that MS is using to remove the toggle from Insiders boggles my mind. They say:
"The new UI has been rolled out to production so it is no longer an Insider feature."
Which is not true. The TOGGLE has been https://docs.microsoft.com/en-us/officeupdates/monthly-channel-2018#version-1809-september-27. Not the new UI as a default.
So, unless the entire point of Insiders having access to the toggle for approx six weeks was to test the toggle and only the toggle (toggle goes on, toggle goes off, toggle goes on, toggle goes off), then Insiders should still have access to it so that they can test what the real point of the testing was: the new UI!
So, now I have to figure out what the Registry value is (assuming there is one) that corresponded to the toggle in order to test the new UI as an Insider.