Man pages matching name sd_bus_add_object_manager in section 3:

sd_bus_add_object_manager.3.en	debian 11 / libelogind-dev-doc
sd_bus_add_object_manager.3.en	debian 11 / libsystemd-dev
sd_bus_add_object_manager.3.en	debian 12 / libelogind-dev-doc
sd_bus_add_object_manager.3.en	debian 12 / libsystemd-dev