Man pages matching name sd_bus_open_user in section 3:

sd_bus_open_user.3.en	debian 10 / libelogind-dev-doc
sd_bus_open_user.3.en	debian 10 / libsystemd-dev
sd_bus_open_user.3.en	debian 11 / libelogind-dev-doc
sd_bus_open_user.3.en	debian 11 / libsystemd-dev
sd_bus_open_user.3.en	debian 12 / libelogind-dev-doc
sd_bus_open_user.3.en	debian 12 / libsystemd-dev