libfclib-dev is declared Multi-Arch: same, but fails to coinstall.
The files
* /usr/lib/cmake/fclib-3.1.0/fclib-config-version.cmake
* /usr/lib/cmake/fclib-3.1.0/fclibTargets-none.cmake
* /usr/lib/cmake/fclib-3.1.0/fclibTargets.cmake
are shared by libfclib-dev version 3.1.0+dfsg-3+b4 as present in trixie
and version 3.1.0+dfsg-3+b5 as present in forky|unstable with varying
content.
Please ensure that shared files have bit-identical content across
architectures, move architecture-dependent files to
architecture-dependent paths or remove the Multi-Arch: same field.
Kind regards
Helmut Grohne