Here is a working hardware combination after several failed attempts – jerky moves, black screen, lost signal, color shifts.
Nikon Z6 – switch video toggle @back of camera for clean HDMI output, set video menu to 60 frames (to avoid display lag), setting c3 standby on. 1800€ incl FTZ.
Sirui VH-10X Fluid, 100€ used.
subtel external power supply for Z6 (only this one allows closing of battery compartment). 56€.
Rode VideoMicro Compact. 88€.
Elgato Cam Link 4K with short USB C connector (to avoid shear stress). 122€.
Macbook Pro with USB-C Digital-AV-Multiport-Adapter (other display port and hdmi did not show up as external display in OBS). adapter 72€.
PW-HT225PIR HDMI Extender with power adapter (USB power alone not sufficient, HDMI amplifier failes consistently). 30€.
30m Cat6 cable. 30€.
Short throw Optoma UHD42 4K Beamer – UHD. 1200€