/usr/include/seqan/parallel/ is in libseqan2-dev 2.3.1+dfsg-4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/seqan/parallel/parallel_algorithms.h
/usr/include/seqan/parallel/parallel_atomic_misc.h
/usr/include/seqan/parallel/parallel_atomic_primitives.h
/usr/include/seqan/parallel/parallel_lock.h
/usr/include/seqan/parallel/parallel_macros.h
/usr/include/seqan/parallel/parallel_queue.h
/usr/include/seqan/parallel/parallel_queue_suspendable.h
/usr/include/seqan/parallel/parallel_resource_pool.h
/usr/include/seqan/parallel/parallel_sequence.h
/usr/include/seqan/parallel/parallel_serializer.h
/usr/include/seqan/parallel/parallel_splitting.h
/usr/include/seqan/parallel/parallel_tags.h