- Like what you've got: stick with it.
- Dislike what you've got: stick with it. Given how good the D850 is, the only reason you'd be in this category is that you picked the wrong camera in the first place. You could just go and pick the right camera and waste the money you put into the D850. But given how well-rounded the D850 is as a camera, I think that unlikely.
- Upgrade to mirrorless: Z8.
The D850 is a better and more well-rounded camera than the Z7II, in my opinion. The Z8 is much more the camera you’re looking for.