I have published an app [Exporter](https://apps.apple.com/us/app/exporter/id1099120373?mt=12) that does something similar - exports Apple Notes to HTML and markdown with the attachments. Give it a try, let me know if it solves your issue.
Also, why did you select JSON as the output format?
Thanks for making your app. I’ve used it more than once and it works well. Many export solutions don’t handle attachments but yours does. So kudos for that.
A few years ago I tried to write my own exporter using AppleScript but got stuck by a showstopping bug in Notes AppleScript implementation. Or so it seemed. I hope that bug is fixed now. I just moved on to use your app instead.
I used AppleScript for the first two years of this app as well (Can't believe it's been 7 years since I started it). But it's hard to handle complex programs, and handing off data to Swift or Objective-C from AppleScript. So I switched to [ScriptingBridge](https://developer.apple.com/documentation/scriptingbridge). It provides better Objective-C APIs to handle Apple Events.
This is so cool and way cooler than my tool!! I chose JSON because it was the easiest option. And also because it is the format I wanted to support first, but mostly because it was the easiest.
A few years ago I tried to write my own exporter using AppleScript but got stuck by a showstopping bug in Notes AppleScript implementation. Or so it seemed. I hope that bug is fixed now. I just moved on to use your app instead.