Awesome initiative!
I wish Apple Notes would support Markdown.
This is my go to app for so much of my life, à Notion style editor would be an absolute game changer.
I'm the author of python library & command line tool, https://github.com/RhetTbull/macnotesapp, that will allow you to use Markdown to create (but not yet edit) notes from the Terminal. I use Vim + markdown to create notes all the time: `notes add -m -e` adds a new note using Markdown by opening the default editor.