After using the Z7 for 5 weeks, it is the focus by wire as implemented in the S-line lenses that bothers me most. The speed-dependent, non-linear (and jittery) MF operation just does not work for me. It is not that focus by wire cannot be done properly; for example the Sony GM lenses have a much better focus by wire implementation by means of linear behaviour (like mechanical lenses) and properly damped focus rings. Also, the Sony A7rIII EVF is much faster in magnified mode, a boon for MF work. (I know, the Sonys have some issues too but that is outside the scope of this thread).
Second thing I don't like is working with a single adapter, it makes changing lenses when both Z-mount and F-mount lenses are used in combination with a single FTZ adapter much more cumbersome. The solution is either to buy more adapters (one for each f-mount lens) or to go back to the D850 body for F-lenses. I did the last.
I am on the second 35/1.8S now, the first one had a bad right edge at far (infinity) distances.