Just want to be sure I'm not missing anything in the reference manual: is it true that the Z6ii isn't able to export pics from installed cards via USB-C cable connected to a computer (in my case to my iPad Pro via hub)? Are the only two ways to transfer images through the SnapBridge app or via card reader? Wifi transfer is taking ages to export 200 image files to my iPad...
My experience is that neither a z7ii or z6ii will import raw files into the Photos app when connected via USBC to either a Mac laptop or iPad Pro. The files are unreadable. Using the memory card from either with a reader works correctly.
Connecting the camera to either device and importing via Lightroom works as expected.
If it does open .jpg's, that sounds as if your file manager program does not know what to do with a .nef file.
You need to tell it which program it needs for opening (I think that is called "associating"), or even to install such a viewer program.
It is now native in linux, but years ago you needed to install a separate viewer program like dcraw, ufraw and more. And tell the filemanager to use that for showing .nef files.
https://en.wikipedia.org/wiki/Dcraw
https://duckduckgo.com/?t=canonical&q=apple+raw+files&ia=web
mentions lots of progs that can do that (mostly commercial :-(.
https://duckduckgo.com/?t=canonical&q=apple+dcraw&ia=web