#1

Currently, the only way to create a note in a folder rather than in the root directory is to use the mouse (sin #1) to right-click (sin #2) and choose New note (sin #3).

Instead, how about specifying a symbol that, when typed at the beginning of a new note title, creates a drop-down for existing folders and, when a folder is selected, puts the new note in that title? It could even be one of the symbols currently excluded because they are not allowed in filenames, such as \.
e.g. Control+N shifts focus to the note title name and the user types \, gets a drop-down auto-fill list, picks the right folder and hits Enter, and then the correct folder is highlighted in the valult File Explorer and the title bar is cleared for the user to enter the note title.

If \ won’t work for technical reasons, you can have a user-definable symbol or character sequence such as zzz activate the folder chooser.

#2

For clarity, that isn’t the only way to create a note in a specific folder. There is an option in preferences to create a new note in the same folder as the current note. So, you can navigate to a note in the folder you want and then create the new note in that folder with ctrl/cmd+n.