There is so much more to photography than pixel gazing. Yes, if you want to, you can clearly see that 48Mp on a FF sensor is more detailed than 24mp on an APSc sensor.
https://www.dpreview.com/reviews/nikon-z6-ii-review#IQ
But for me anyway, that's one of the least important factors in choosing a camera. I have made a lot of pics over the years and the 'best' have been from cameras with both APSc 12mp sensors and FF 24.
Some specialist areas do benefit from resolution ofc, and in Macro work I often wish for a few more Mps, but in general I regard Dynamic range, Colour rendition, Ergonomics, Weather sealing, Battery life, Lens quality and range, Autofocus performance and Weight to matter more to me.
On the Dynamic range front, I do trust DxOMark testing. Of all the cameras mentioned here, the results in the sensor 'landscape' test (the best measure of dynamic range in practice) are:
Nikon Z7: 14.8
Z6: 14.3
D850: 14.8
D610: 14.4
The best camera they ever tested? Hassleblad's X1D 50....14.8 also but overall
They don't test Fuji, but the APSc benchmark is the D500 and it scores 14.0, which is probably around where the Fuji will be.
If 15 is 100% benchmark, then the Z7's 14.8 is 98.6%
And the Z6? 95.3. Who honestly is not going to buy a camera for that 3%...a little skill if exposure and photoshop resolves the issue in any case.
As to resolution, go to Flikr and look at the Z6 photogroup images.
https://www.flickr.com/groups/nikonmirrorless-z6/pool/
It's like cars...yes, there are faster cars than yours but if that spoils your pleasure in what you have, then that's YOU, not the car and honestly if that is you, forget this thread, and just save for the best (and repeat next year when your best is bettered
).