Gotta agree with others here. I have a Z6 and it breaks up pretty much regarding noise at 6400ISO. I have used 6400 but with a much darker exposure to purposely replicate a dark scene. A full second would have brought the ISO down to 800 which is much closer to native and would have been my first move. A smaller aperture might have helped too but that lens is pretty sharp at 4.5. Hard to say too much looking at something posted here per the reduced resolution in posting. A simple contrast increase might be a bit difficult as the gradient of much of the buildings is very close to that of the sky. To really make it "pop" some creative editing would probably be necessary, color grading the sky differently that the buildings. If you want to have another go at it, exposure bracketing might help zero in on the best exposure.