/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/ is in libslepc-complex-3.7.3-dev 3.7.3+dfsg1-5.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcbv.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcds.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepceps.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcfn.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcmfn.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcnep.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcpep.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcrg.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcst.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcsvd.h90
/usr/lib/slepcdir/3.7.3/x86_64-linux-gnu-complex/include/slepc/finclude/ftn-auto/slepcsys.h90