Going the other way, I've just upgraded from micro 4/3 to z6, where I considered fuji as well in the decision process.
Eventually ended up with Nikon, because
1. IBIS is important to me and the only stabilized fuji, the x-h1 is actually bulkier AND weighs more than the equivalent z6 configuration:
https://camerasize.com/compact/#772.448,795.784,ha,t
2. 4/3 to APSc is not a giant leap in terms of DR/Noise, about 1/2stop, whereas there is 1+stop difference between APSc and FF. If you don't have to carry much more weight (see point #1), there is little reason to stay on a crop format.
3. In-house adapter provided cheap in the kit, recent f-mount lenses work as good as native glass on it! 3rd party manufacturers (sigma and tamron) recognized the FTZ platform and keep adjusting their firmware to stay compatible. Elsewhere (fuji, sony) the adapter manufacturer is a completely separate player, has to keep his FW up to date towards both sides.
4. Z-mount lenses are really, really impressive.
5. Price difference isn't really huge. Actually the nikon can be cheaper at system level... The
z6 body+FTZ adapter + 64GB QXD card(!) costs 1600€ , while the
x-t3 body alone is 1400€. And you have to add a 300+€ adapter if you want to try and 3rd party lenses on the Fuji. Looking at
equivalent lenses: 1.2/56 is almost
1000€ , where the nikkor z
1.8/85 is 850€ minus a 100€ discount, same goes between standard zooms, fuji 2.8/16-55 and the really good performer z 4/24-70. All in all, it seems actually cheaper(!) to build an equivalent system on FF while you have the opportunity to grow or keep "average" glasses for some purposes and top ones for your focus areas.
What I am missing from the nikon body are the superior video features of the x-t3.