Nikon Z8 User Manual page 321

Deleting All Pictures
1
Choose a memory card.
Press 1 or 3 to highlight the slot containing the memory card
from which the pictures will be deleted and press J.
2
Delete the pictures.
A confirmation dialog will be displayed showing the name
of the folder containing the photos to be deleted. Highlight
[Yes] and press J to delete all pictures from the folder. The
folder is that previously selected via [Playback folder] in the
playback menu.
Note that depending on the number of pictures, some time
may be required for deletion.
247
Deleting Pictures