Renaming Note titles in Apple Notes.

This is not possible.

You have a basic misunderstanding. Notes do not really have formal titles. They do have a “Title” format that may be applied to a portion of a note. But that portion is included in the note, just as all the parts formatted differently are.

The first line of text, within an individual note, is effectively the title of the note. As such, the displayed title can only be altered by changing the text within the body of the note.