Not sure how it would be a zero-day exploit.. you're allowed to run whatever code you want on your Mac, and if you bypass the sandbox by giving Full Disk Access or whatever other permissions this uses, it follows that it will be able to read your iMessage database.

As for the iPhone bridge, that does use a jailbreak which is, of course, an exploit--one that Apple has patched and the patch deliberately not applied to the device in question.