It looks as though you’re looking in the wrong place.
The first of your images shows the ‘Quick Capture’ panel. I’ve changed my keyboard shortcut so it’s no use me telling you what to press, but look in preferences (cmd ,) to see what ‘Quick Capture shortcut’ is mapped to. Press this key combination to invoke this quick capture screen; which is a great way to create a quick note without opening the main app.
Your screen shot shows, I think, a note/draft typed into a draft within the main app. The options you’re after: append, prepend, etc aren’t available here. My understanding is that actions (as available in the iOS app) are coming… but not yet. At that time it would, I’d think, be able to do such things from the main app.
For now though… give the Quick Capture a go. It’s really ever so useful.