Using the default widget for bookmarks currently allows inherited bookmarks to be deleted (accidently).
Currently the Guide says "If the bookmark is inherited from the web map, the Delete button is unavailable."
This does not seem to be working.
The only way to get them back is to go to your browser options, delete history and delete tracking protection...
For general map users this is a lengthy process and hard to find.
Changing the widget to offer app administrator the option to disable the delete button
A new button to restore app default bookmarks (without effecting any user created bookmarks)
would enhance the widget and make it a reliable app tool.