I have a Nikon Z7, I bought it when it first came out. I consider that camera a landscape/nature camera. I use my Z8, I have two, for wildlife and did use a Z9. For wildlife I like a fast camera with high fps and a large and fast buffer rate, this makes shooting a lot easier. I started photographing wildlife with a D800 and then later on with a D850, I learned the differences in different camera uses along the way. There was some frustration on my part with the slower cameras. Here is what one review said, "
Generally good performance for its class, but somewhat limited buffer." I learned quickly that the buffer was very important in wildlife photography. I've included the review below. I think you start out shooting with what you have, learn about wildlife photography, and then along the way you figure out what works for you and what your equipment needs are. If it's portrait type shots the Z7 is fine, if you get into wildlife in action shots it may be a bit slower and less accurate than some of the newer Z cameras. I love the Z8, which is why I bought the second one, but I found the Z9 a bit heavy and bulky so sold it once I tried out the Z8. I still use my Z7 as a lighter camera for landscape/nature shots.
https://www.imaging-resource.com/PRODS/nikon-z7/nikon-z7A6.HTM