MG Audet wrote:
Yes, it can take/read CFexpress cards. If the D850 is a few years old you will need to do a firmware upgrade to read the card. You will also need a card reader rated for the new card. My old Sony reader was good for XQD only. You can check whether or not your camera is updated in the Menu/Tools, last item "firmare". If it show 1.2 you are good for CFexpress, if not you will need to upgrade your firmware.
Good luck,
Michael
Does the CF reader read the XQD cards you may still have images on, or may use for backup?