Nikon Z9 Mirrorless Camera - Manual (Page 250)

250 Protecting Pictures from Deletion
D Voice Memos
Protecting photos also protects any voice memos recorded with the pictures.
Voice memos cannot be protected separately.
D Caution: Uploading Protected Pictures via FTP
The copies on the FTP server will not be protected even if the originals are.
Markings can be added using ratings.
A Removing Protection from All Pictures
To remove protection from all pictures in the folder or folders currently
selected for [
Playback folder ] in the playback menu, press the g ( Fn4 ) and
O ( Q ) buttons for about two seconds during playback.