Someone here actually helped me with it.

Automate the process:

There are several scripts that automatically take the Sinology .NSX export you just created, then they translate all it’s content into .md files that you can then easily import in one-click into Joplin. Here are the ones I’ve found: https://github.com/Maboroshy/Note-Station-to-markdown/ “It creates md files and puts all attachments into a sub folder.” https://github.com/xinbindai/Note-Station-to-Joplin A customized version of the above script “to export notes/images in markdown + Front Matter (Directory) that can be [more] easily imported into Joplin.” https://github.com/andreas-vester/notestation-to-joplin This script might be worth it if the above scripts don’t work. Some people had issues with this script, but managed to mostly fix them. See here. Copy-paste each note:

This sounds tedious at first, but once you get in the flow, it isn’t that bad. It isn’t doable if you have 10’000+ notes, but in my case, I got it in a few hours. Remember that even if it takes you one hour a day for a week to move them all, since you’re switching to a nonproprietary format you only have to do this once and then you’re set for life. This person on the Synology forum had your same problem and ended up choosing this option.