OK, downloaded the latest lensfun sources, built and installed. Ran the update Python script. Now I can see my lens in 2 files:
~/.local/share/lensfun/updates/version_1/mil-nikon.xml: Nikkor Z 24-70mm f/4 S
~/.local/share/lensfun/updates/version_2/mil-nikon.xml: Nikkor Z 24-70mm f/4 S
But the lens is not recognized automatically in RT and when I tried to select it manually I don’t it listed. I guess I need somehow to tell RT to look for the new lensfun database?