Man pages matching name sd_bus_message_peek_type in section 3:

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