Man pages matching name xcb_input_get_device_modifier_mapping in section 3:

xcb_input_get_device_modifier_mapping.3.en	debian 10 / libxcb-doc
xcb_input_get_device_modifier_mapping.3.en	debian 11 / libxcb-doc
xcb_input_get_device_modifier_mapping.3.en	debian 12 / libxcb-doc