TL;DR: adjustable by default. If you want to lock it to a specific voltage, cut the line above ADJ and solder across the pads next to the voltage you want.

Source: https://www.qskj.cc/shop/product/1941621-mini-dc-dc-buck-step-down-module-4-24v-12v-24v-to-5v-3a-power-module-qs-1205cme-3a-79148