B&H sells an adapter for the Olympus OM lens to Nikon Z camera:
Buy KIPON Olympus OM Lens to Nikon Z Mount Camera Adapter featuring Maintains Infinity Focus, Aluminum and Brass Construction. Review KIPON null
Like many internet reviewers, I would take KR's comments with a grain of salt.
Before you rely on ANY reviewer, you have to study the reviewer, to determine their bias and point of view. If it matches yours, OK. If not, you have to filter what they say.
There is another reviewer that I now usually ignore, because of his bashing of any camera with a smaller than FF sensor.
Staying with Nikon dSLR; the older D810 or current D850.
Or going Nikon mirrorless, with the Z cameras.
One catch with the FTZ adapter on the Z. It will ONLY autofocus the electronic AF-S and AF-P lenses. It will NOT autofocus the mechanical AF lenses (the ones that have the AF screw on the mount).
Canon mirrorless R is a good option to the Nikon Z.
But the 800 pound gorilla in the corner of the room is Sony. And Sony has become a serious competitor.
Sony has many more generations of mirrorless cameras, and have refined the cameras. Nikon and Canon are only into their 2nd generation of FF mirrorless cameras.
The Sony lens landscape has matured to be about where the Nikon and Canon dSLR lens landscape is. And it is Nikon and Canon mirrorless lenses that are lacking, where they need to use some of the dSLR lenses on the mirrorless cameras.
About the Nikon Z and Canon R lens landscape.
The mirrorless lens systems are a "work in process." Not all of the lenses are available, and some will not be for years.
If they have the lenses that you want, then that is not an issue.
But if the lens that you want is not available in native Z or R mount, then you have to use a dSLR lens via an adapter on the Z or R camera. Or, WAIT until the lens becomes available in the native Z or R mount.
About the APS-C mirrorless cameras.
I know nothing about the Fuji cameras.
But, historically, both Nikon and Canon have positioned the APS-C cameras as consumer grade cameras. And if you want PRO grade lenses, there were maybe 1 or 2, otherwise you had to put a FF lens on the APS-C camera. And the selection of APS-C lenses is disappointing.
Example1: I have a FF Nikon 70-200/4 on my APS-C Nikon D7200, for that exact reason. There is no production APS-C equivalent lens to the FF 70-200/2.8, which would be a 45-135/2.8. The closest is the FF Tamron 35-150/2.8-4.
Example2: The only Nikon dSLR APS-C prime is the 35/1.8 normal lens. Canon APS-C does not even have this lens, but they have other primes.
Having said that, over time, the consumer grade lenses have been getting better and better. And some are quite good.
So based on history, I do not expect the Nikon or Canon APS-C mirrorless systems to be any better than their dSLR counterparts were. And with the emphasis on the FF mirrorless, I think it will take quite some time for their APS-C camera line (including lenses) to get up to speed. Although Canon had a headstart here.