While I happily sing and prance in Apple’s “Walled Garden” and have done so for over a decade, I feel uneasy about putting all of my notes in Notes with no easy export option.

You can use Exporter from App Store to export to markdown notes.

https://itunes.apple.com/app/exporter/id1099120373?l=en%26mt...

You can AppleScript the contents out if you’re desperate, but there’s a SQLite database that you can pull the data from as well IIRC.