Nikon Z 9 Reference Manual page 501

D
Cautions: Folder and File Numbers
•
When the current folder number reaches 999, the camera will no longer be
able to create new folders and the shutter release will be disabled if:
- the current folder contains 5000 pictures (in addition, video recording
will be disabled if the camera calculates that the number of files needed
to record a video of the maximum length would result in the folder
containing over 5000 files), or
- the current folder contains a picture numbered 9999 (in addition, video
recording will be disabled if the camera calculates that the number of
files needed to record a video of the maximum length would result in a
file numbered over 9999).
•
If there is space on the memory card, you will nevertheless be able to
continue shooting by:
- creating a folder with a number less than 999 and selecting it as the
storage folder, or
- changing the options selected for [Frame size/frame rate] or [Video
file type] before recording videos.
D
Startup Time
Additional time may be required for camera startup if the memory card
contains a very large number of files or folders.
C The Photo Shooting Menu: Shooting Options
501