Theme Preview does not work on any themes

Hello I am having a strange issue with WP 5.4.1
I’m trying to preview Themes but none of the previews work.
At one point I tried previewing the latest Twenty Twenty theme and I got an error saying “I was not authorized” and yet I am the Admin / Super Admin, so I am not sure what’s going on… when I reloaded and tried again, the customization sidebar appears on the left but the theme does not preview/change (I see my old theme).

The page I need help with: [log in to see the link]