Nikon Z 8 Reference Manual page 69

Tip: Using the i Menu with the Camera in "Tall" Orientation
When the camera is rotated to take or view pictures in "tall"
(portrait) orientation in photo mode, the i menu displays in the
monitor and viewfinder rotate to match. In video mode, only the
playback i menu rotates to match camera orientation.
69
The i Button (i Menu)