Nikon Z8 User Manual page 720

f4: Control Lock
Lock exposure settings or focus-point selection.
Option
[Shutter speed lock]
[Aperture lock]
[Focus-point lock]
Select [ON] to lock shutter speed at its current value in modes S and M.
O icons appear in the shooting display and control panel when shutter-
speed lock is in effect.
Select [ON] to lock aperture at its current value in modes A and M.
O icons appear in the shooting display and control panel when aperture
lock is in effect.
Select [ON] to lock focus-point selection on the currently-selected focus
point.
Focus point lock does not apply when [Auto-area AF] is selected for
AF-area mode.
When [3D-tracking] is selected, the focus point will track subject motion
while the shutter-release button is pressed halfway.
G button U A Custom Settings menu
Description
646
f4: Control Lock