I've used carnauba wax on shell stones, and on a YMI shin-kaya board, and it worked just fine.

That said, I also found some micro-crystalline wax recently and used it on another board and some bowls that had been really, really abused. After removing the old finish with an abrasive "magic" sponge a light coat of the wax made the bowls look good again (the board hadn't been in bad shape, but the wax had been rubbed off in places). It was easier to apply a thin coat with the micro-crystalline stuff than with carnauba. I used a brand called "Renaissance" and it was kind of expensive. This brand is basically the same thing and is much more affordable:

https://www.amazon.com/dp/B07FCPBX83/

Those bags look cool, and probably protect the shell from oils in the wood, or something like that? I've never seen anyone use them, though.