I have many notes in many notebooks with many tags. Sometimes I have the leftmost pane (sidebar) scrolled to where the tags are, so I cannot see the list of notebooks and therefore cannot see which notebook is selected. I cannot tell which notebook the current note is in. That is a problem.
One solution to this is to put the name of the current notebook in the title bar of the current note, perhaps to the left of the date. That would be sufficient for my needs. Another solution is to put the notebook in the window title, as suggested in much of the previous discussion here. If you are going to put the notebook in the window title, then it probably makes sense to include the note title also, so that Windows taskbar shows it (and when you use Alt-TAB and similar). And perhaps the profile, etc, as others have suggested. And then perhaps this should all be user-settable via some Options settings. But like I said, simply adding the notebook name to the note header would be fine with me.