You asked
Should I upgrade from the nikon z7?
Probably not, at least not for the sensor. The Nikon Z7 II has the same 45.7-megapixel full frame sensor and in-body stabilisation as the Nikon Z7. The only difference I can confirm is the announcement date, 2020 against 2018. If your files already do what you need, the money will do more elsewhere.
The Z7 is still a good used landscape camera. If you do want to change bodies, buying used is the smart route, since a body one generation old gives you most of the camera for much less. For landscapes, I'd spend on a sturdy tripod or a circular polariser before a new body. You'll find both in the landscape kit.
Written by Claude from this site's pages.