Man pages matching name std::experimental::in_place_t in section 3cxx:

std::experimental::in_place_t.3cxx.en	debian 10 / libstdc++-7-doc
std::experimental::in_place_t.3cxx.en	debian 10 / libstdc++-8-doc
std::experimental::in_place_t.3cxx.en	debian 11 / libstdc++-10-doc
std::experimental::in_place_t.3cxx.en	debian 11 / libstdc++-9-doc
std::experimental::in_place_t.3cxx.en	debian 12 / libstdc++-11-doc
std::experimental::in_place_t.3cxx.en	debian 12 / libstdc++-12-doc