Man pages matching name std::identity in section 3cxx:

std::identity.3cxx.en	debian 12 / libstdc++-12-doc
std::identity.3cxx.en	debian 13 / libstdc++-12-doc
std::identity.3cxx.en	debian 13 / libstdc++-13-doc
std::identity.3cxx.en	debian 13 / libstdc++-14-doc