I think the root cause may relate to the the way Samsung’s app attempted to duplicate my original file database and environment when I migrated my data from my previous Galaxy. Looks like a code bug to me. Others have reported similar symptoms with other Galaxy models over the last several years.
Since I got my S21 Ultra I notice that in Explorer, most folders display as duplicated pairs. It’s as if they’re crosslinked in the file system (or the driver’s emulation of the file system in Explorer). If I delete either copy/image of a folder in Windows, the original folder is deleted in Android. If I then create a new folder by the same name, only one copy of that folder is displayed. Both images in Explore have exactly the same properties.