To my mind, it has to be a configuration option.
Here's why:
When you create a new note, it opens a new window (Windows 10, at least).
That's great, because there is lots of room to edit.
When you double-click a note, it opens in a new window. (Also great.)
It's handy to have multiple windows open, so you're not constantly navigating
back and forth to different notebooks.
Now then, open a note in notebook A. Then open one in notebook B.
Finally, revisit the window for the note in notebook A.
As you're editing that note, realize that you want to break in two. Hit Ctrl+N,
and copy stuff into it. Terrific.
HOWEVER: The new note does not get saved in notebook A (the one that
contains the notebook you were editing). Instead, it gets saved in notebook B
(wrong notebook!).
I can see the utility of a working style that says all new notes go to a default "inbox"-style
folder, where you sort them later.
But personally, I'd like to see new notes "follow" the current note, the same way new files
in NotePad++ follow the currently open file into the folder the contains it.
The only behavior that doesn't make sense to me, is the "last opened folder", because if
you have notes opened from several folders, you may not recall which folder that was.
But I admit that it may work well for people who don't open many windows.
The only reasonable solution I see is a configuration option that allows for all three behaviors.