Man pages matching name xmvacreatesimplespinbox in section 3:

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