This is very much true. You'll never get the camera support in FLOSS software like a dozen paid professionals can do, also with getting help from the manufacturers.
But it's not always that big a deal.
At least the basic camera support is pooled together between several FLOSS developers. (See: raw.pixls.us) Rawtherapee hasn't seen a meaningful update in years so judging this one project is not 100% accurate view of the whole FLOSS softwarescape.
Screenshot Windows Installation Instructions Just open the zip file and run the executable installer. Linux Installation Instructions Software should be installed through your distribution’s package manager. If RawTherapee 5.9 is not yet available in your package manager, you can use the AppImage: Download it. Make it executable: chmod u+x RawTherapee_5.9.AppImage Run it: ./RawTherapee_5.9.AppImage macOS Installation Instructions We don’t have a macOS build available just yet. One will be upload
Raw Therapee V5.9 was out in Nov 2022, has support for the Z5, Z6-II, and Z7-II. I guess that means the .NEF files. a .DCP is not included, the newest being the "Nikon Z7.dcp". Interesting that ART has more .DCP files, fortunately the two are compatible.