Man pages matching name hwloc_topology_diff_u in section 3:

hwloc_topology_diff_u.3.en	debian 10 / libhwloc-doc
hwloc_topology_diff_u.3.en	debian 11 / libhwloc-doc
hwloc_topology_diff_u.3.en	debian 12 / libhwloc-doc