Man pages matching name xmvacreatemanagedlabelgadget in section 3:

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