What to expect when activating this theme:
In Appearance > Themes, a message that this theme does not support the customizer and you will use the new (beta) Site Editor for customizations.
New Editor. Notice Customize does not appear. It comes back when you activate any other theme. You will also no longer be able to edit a menu section. Each page created will appear as a link in the navigation section of the header.
There are several new patterns with this theme that users will find helpful in laying out their pages. Find these by going to Appearance > Editor > click the blue plus + sign and toggle to Patterns.
Two helpful reviews and examples for the theme:
Helpful review and examples for using the theme – https://wordpress.com/theme/twentytwentyone