The Z lenses are for the mirrorless bodies and only work on the mirrorless bodies. https://www.nikonusa.com/c/lenses/mirrorless-lenses/overview
As long as SLR bodies are produced, Nikon will continue to make SLR lenses (and probably for a while afterwards)
https://en.wikipedia.org/wiki/Nikon_D6 was released in 2020.