There are different Notebookbar implementations available to switch from one to another should be as simple as possible cause first the user has to test them and it should be easy to switch back.
Therefore the .uno:ToolbarMode comment should be available as dropdown menu everywhere. first in the notebookbarshortcuts.xml file and than also as GtkToolButton in an sfxlo-NotebookbarToolBox.
Yes, would like it consistent across each NB flavor. But should it go to the configuration menu (gear | hamburger) or needed as a split button on all NB views?
It's requested in the HIG. So this ticket rather discusses how and where to place the control, right?