Nikon Z 9 Reference Manual page 307

D
Zoom
•
The camera display can be zoomed in by pressing the X button during
recording, but this has no effect on the footage output to the recorder.
•
If no footage is currently being recorded, changes to zoom using the X
button will be reflected both in the camera display and in the output to the
recorder. The output resolution however switches to [1080p
(progressive)], even if the option last selected for [HDMI] > [Output
resolution] in the setup menu was [4320p (progressive)] or [2160p
(progressive)].
Recorders
307