I do understand you want to avoid menu clutter, but I think splitting a note would be much more convenient that copy and paste in some scenarios - especially if there was a keyboard command, perhaps even a markdown type command like ===== splitting a note and putting the first line of the text below into the title field of the new note.
I see it being particularly useful when one is arranging a lot of information that one has captured quickly, eg notes of a meeting or a braindump, where you don’t want to waste time or to lose focus, by worrying about making sense of what you are writing, you just want to get it down.
In those circumstances I end up with a long note and then then copy and paste within the note and add headings to structure it. The very last job would be to hitting ==== to split the note would be fast and intuitive. At that point creating new notes and copying pasting feels like a lot of unnecessary work.
But I may be doing special pleading for a rare use case!
Look forward to seeing how Agenda evolves. Agenda is an essential part of my workflow and apart from some things already in the ‘features we are working on’ list, it’s prety much ideal! (Apart from splitting notes )