Photo Above Data [NIKON Z 6, Sigma 24.0-105.0 mm f/4.0 ART, ISO 16000, ƒ/6.3, 1/200, Focal Length = 95]
I have owned the Fuji X-E series cameras for a few years. I love them. Then I bought the Nikon Z6 to be able to shoot mirrorless with some of my Nikon glass.
I think the Fuji X-E3 compares pretty well to the Nikon Z6. I like that the Fuji X-E3, when you are close to someone will find their face and eyes.
The Nikon Z6 camera automatically detects the subject and selects the focus area. At default settings, the camera gives priority to portrait subjects; if a portrait subject is detected, the selected subject will be indicated by a yellow border (if multiple faces are detected, you can choose your subject using the multi-selector).
To get some photos from the service, I left the 55-200mm on the Fuji X-E3 and the 24-105mm on the Nikon Z6.
No question that the larger full-frame sensor on the Nikon Z6 had less noise. However, I was also pretty happy with the noise on the Fuji X-E3.
I think that the dynamic range is better with the Nikon Z6. You can see some of that comparison here.
I love the smaller size and weight of the Fuji system. I think the quality is excellent.
I think that the image quality and higher ISO are definitely in favor of the Nikon Z6.