ProNotes Markdown Plugin for Apple Notes

If you have a lot of date saved in the default Apple Notes app and you
aren’t interested in migrating to Obsidian, Notion, Joplin or Evernote,
you still don’t have to settle for the limited formatting and back
linking options you are provided. ProNotes, a free app, allows you to
use standard Markdown syntax, if you choose to, in order to format your
text.

You can also choose to use a floating
toolbar with formatting tools. You can even use slash commands for
titles, headings, code blocks, checklists, numbered lists and even
tables.
Bi-directional links
macOS Sonoma introduced the ability to link
to other notes. ProNotes
allows you to view all notes linking to the current note via the
Backlinks feature.