Nikon Z8 User Manual page 711

"Save to All"
1
Assign [Recall focus position] to a control.
Repeat this step for each of the controls you intend to use for
memory recall.
2
Select another control in the custom control list and, when
prompted to choose a role, highlight [Save focus position]
and press 2.
Save options will be displayed.
3
Highlight [Save to all] and press J.
4
Focus on the desired subject in the shooting display and
press and hold the control to which [Save focus position] is
assigned.
A F icon will appear in the shooting display if the operation
is successful.
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f2: Custom Controls (Shooting)