librsvg-2.54.5 has that in the upstream tarball -- the part removed by:

%if 0%{?bundled_rust_deps}
# Use the bundled deps
%else
# No bundled deps
rm -vrf vendor .cargo Cargo.lock
%cargo_prep
%endif

i.e. ".cargo" is a directory including ".cargo/config" for vendoring.

However, it looks like newer versions *don't* including vendoring, so
that will have to be added and configured separately.
(Run "cargo vendor", tar that vendor/ as an additional Source, and write
a .cargo/config for it.)

Thanks, that helped. Now at the final linking command I get [1]:

 = note: /usr/lib/gcc/i686-w64-mingw32/13.0.1/../../../../i686-w64-mingw32/bin/ld: unrecognized option '--package-metadata={"type":"rpm","name":"mingw-librsvg2","version":"2.56.0-1.fc39","architecture":"x86_64","osCpe":"cpe:/o:fedoraproject:fedora:38"}'
          /usr/lib/gcc/i686-w64-mingw32/13.0.1/../../../../i686-w64-mingw32/bin/ld: use the --help option for usage information
          collect2: error: ld returned 1 exit status

I can't really find any hints where --package-metadata coems from, is this a rust thing?

Thanks
Sandro

[1] https://download.copr.fedorainfracloud.org/results/smani/mingw-librsvg2/fedora-rawhide-x86_64/05748925-mingw-librsvg2/builder-live.log.gz