Well that's certainly fair. However in the case of both Joplin and Zim (and probably others), notes are either stored in or can be trivially exported to plain-t

Well that's certainly fair. However in the case of both Joplin and Zim (and probably others), notes are either stored in or can be trivially exported to plain-text formats. Joplin's native, lossless backup format is just markdown in a tarball. Both are also open source.