Nikon Z8 User Manual page 688

e3: Exposure Comp. for Flash
Choose how the camera adjusts flash level when exposure compensation is used.
Option
[Entire frame]
YE
[Background only]
E
The camera adjusts both the flash level and exposure. This changes
the exposure for the entire frame.
Exposure compensation is adjusted for the background only.
614
G button UA Custom Settings menu
Description
e3: Exposure Comp. for Flash