The Z7ii makes an excellent landscape camera. The autofocus may hold you back if you are doing wildlife, especially moving wildlife, but is more than adequate for stationary subjects. One advantage is that it has a 46 MP sensor, this will allow you to crop significantly, or print large prints.
One caveat, if you plan to use the lens you have on your D3400, you will need an FTZ adapter. This runs about 300 USD. Additionally, the lens you have is probably a DX lens. That means you will only be using about half of your sensor. If you buy new, you can purchase a kit and get a discount on the kit lens. The Z 24-70 f/4 is one of those. It will add about 600 USD to the package (saving about $450 over purchasing the lens separately), and save you the 300 USD you would have to spend on an FTZ. Additionally, it is a full frame lens capable of giving you the full resolution of your camera, and is an S-line lens.
Currently the Z7ii is on sale for $1900 body only, $2500 with Z24-70 F4 lens. The Z24-70 F4 runs $1050 when purchased separately.
Not sure what prices in your country run.