Man pages matching name xmvacreatemanagedcombobox in section 3:

XmVaCreateManagedComboBox.3.en	debian 10 / libmotif-dev
XmVaCreateManagedComboBox.3.en	debian 11 / libmotif-dev
XmVaCreateManagedComboBox.3.en	debian 12 / libmotif-dev