Considering submitting a feature request to the GitHub repo for this, but let’s just ask here, first… ![]()
Both the Files 
 app and the Bookmarks 
 app support tags 
 , but they don’t share their list. At least, I have done some tests and haven’t succeeded.
What I would really like is, that any tag I use somewhere within my Nextcloud, is shared across all apps from the Appstore. And that a search for a tag is done globally across all data in my Nextcloud account.
So question for @marcelklehr is, would it be possible to re-use the tags from the Files app in the Bookmarks app?