You do not sync
any Kindle whatsoever over USB. The Kindle will automatically sync at regular intervals over WiFi.
Unless you mean with calibre. In which case, plugin your device, and if it shows up in the toolbar you can send books. If not, post a debug log in
the calibre forum here:
https://www.mobileread.com/forums/forumdisplay.php?f=234
Instructions for doing so are here:
https://www.mobileread.com/forums/sho...d.php?t=118560