thanks to Gregor Dawdle for this tip, but it doesn't work for me in OVF mode :-(
the brightness of the display superimposed on the OVF, can also be adjusted. By QMenu "LCD brightness" if you have the eye in the viewfinder. Indeed, adjustment of brightness OVF and EVF / screen are seperated.
Kind Regards and thank you for all your curation.
Via Thomas Menk