- Like what you've got: Of course you do, stick with it.
- Dislike what you've got: Stick with it. Not exactly sure what you dislike. The only realistic side-grade path is the D850, which means you bought the wrong camera in the first place. Your other choice is to switch to a Canon 1DX Mark III or Sony A9 Mark II. Moving to a D850 you'll be giving up body build, vertical grip, battery endurance, and more. You’ll be changing to Canon lenses and controls if you get the 1DX Mark III. You'll be changing to Sony lenses and control if you get an A9 Mark II, and again you'll give up body build, vertical grip, and battery endurance.
- Upgrade to mirrorless: Z8 or Z9.