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.
Pratik Agree. As much as Apple has improved Notes in the last few years, I still hesitate to use it as my primary notes-taking app.
Brad Barrish I agree, but there's nothing that comes close for me and my wife to collaborate quickly and easily on things like grocery lists, email drafts and shared notes. But to your point, there are often times when sync simply doesn't work and it's infuriating.
Lou Plummer ProNotes adds Markdown support to Apple Notes
Manton Reece @bradbarrish That’s true, for sharing and editing with a couple people, Notes is pretty good. I bet it replaced Google Docs for a lot of people for shared lists, etc.
Matt Huyck This problem is exactly why I won’t use Notes for anything important. It’s just not a serious app without interoperability of any kind.
Aeryn I like Notes but it’s a walled garden. So I only use it for very temporary things
Dan Alcantara For me, Notes exists solely as a way to let my family know what the meal plan is for the coming week. I tried using it as my actual place to keep information and I like it but that niggling feeling in the back of my head that all of this could just disappear kept me from fully committing, despite my wife and kids having zero issues with it.
Manton Reece @aeryn Same here on the temporary use. I occasionally use it to ask Siri to transcribe something while I’m driving, then I copy and paste it out.
Craig Morgan @manton on a side note, the #obsidianmd team/community spent some considerable effort on an importer for other formats to Obsidian (which of course uses an open markdown file based storage natively), to enable migration from many notes platforms in. Amongst their successes is a very good Apple Notes import, which now handles a *lot* of idiosyncrasies and happens to leave you with a lovely folder full of clean separate md file per note … might be handy until Apple relent…
Craig Morgan Manton Reece @craigmorgan That sounds great. Obsidian folks doing good work.
Jade van Dörsten I really like the "File over app" philosophy championed by Obsidian's CEO https://stephango.com/file-over-app
Manton Reece 
James Manes Agree with these thoughts. I'm interested to see what Proton does now that they have acquired ("teamed up with") Standard Notes.
Javier Plumey As much as Obsidian touts the file over the app, the plugin ecosystem really ties you down into Obsidian as soon as you get into any advanced functionality. I moved off Obsidian because I was spending more time fiddling with plugins than getting the most out of my notes. Also, the mobile experience was never really good. And I found it strangely difficult to share notes with people. Even a basic copy and paste with formatting never really worked well. Anyway, I’d love more import/export options with Apple Notes, and for them to fix bugs around Shortcuts.
Tevin @manton like many other note taking apps, Apple Notes was never intended to be exported as a whole, it keeps users’ data locked within the ecosystem.
Roger Scrafford @bradbarrish I've had Apple Notes betray me more than once, probably because of some iCloud business. I seem to have too many Apple devices for iCloud to support. I had to laboriously export / delete / import ALL my files in order to resume sync across device.
Yury Molodtsov @manton There are third party apps that can export Apple Notes, thankfully
Matt Huyck @craigmorgan Thank you for the reminder that this exists! Obsidian is what I use instead of Notes, so I need to export the old notes I still have moldering away on iCloud.