In a blog post about Journal, John Gruber makes a detour to highlight the lack of full import and export in Apple Notes:
I worry that import and export aren’t priorities for Apple. Apple Notes can import RTF and plain text files, but its only option for exporting is, bizarrely, PDF — which is a file format Notes can’t import. A good system for import/export would allow for full fidelity round-tripping. You should be able to export to a file or archive format that Notes can also import, without losing any formatting, metadata, or image attachments. Notes doesn’t even try.
That’s a no-go for me. I’m now using Micro.blog for notes, and I wouldn’t even consider anything without Markdown import and export. Of course Apple isn’t going anywhere and I expect Notes to be supported essentially forever in some form, but iCloud sync is opaque. If there’s ever a hiccup, I want a backup of the actual plain text files.