From the flight notes!
We are introducing a simplified Windows Insider Program Settings page via Settings > Update & Security > Windows Insider Program with Build 18317. The goal is to make the end-to-end experience of signing up for the Windows Insider Program and setting up your PC to take new builds much easier by simplifying the experience and removing some of the clutter. You’ll find that all the same functionality is still there.
And here it is, in beautiful Black theme of course :/
Under ‘Pick your Insider settings’ are the choices.