Took the Z9 and 800mm out for round a few days ago. My traditional hotspot for critters was notably slow and it took hours to find some subject matter to point the rig towards. I'm still working to dial in the camera to my tastes and still haven't had a good chance to try some high ISO shooting which is sort of an important part of what I tend to shoot. My lack of subject matter left me shooting the moon just for a "how sharp is this lens on this camera shot".
I'll add that I haven't quite figured out the noise profile of this camera either. With the D5/D6 I knew exactly what to expect so this one is still not quite dialed in.

NIKON Z 9 VR 800mm f/5.6E lens 800mm f/8.0 1/50s 450 ISO +0.7 EV

NIKON Z 9 VR 800mm f/5.6E lens 800mm f/5.6 1/200s 64 ISO 0.0 EV

NIKON Z 9 VR 800mm f/5.6E lens 800mm f/6.3 1/640s 160 ISO 0.0 EV

NIKON Z 9 VR 800mm f/5.6E lens 800mm f/5.6 1/500s 250 ISO 0.0 EV