I don’t accept free USB sticks anymore, although I have sometimes wondered whether I might be safe with one from a reputable vendor (HPE, Microsoft and so forth) - although the reputable vendors don’t seem to hand them out anymore.
Even with fresh, sealed in box, USB sticks I plug them into a non-network connected Raspberry Pi which automatically repartitions and formats any drive plugged into its USB port. If it’s an obvious bit of malware, this will wipe it. If its one of those electrocution gizmos, I don’t care (it’s a Raspberry Pi! Nice n cheap!) Of course, there are more insidious ways of compromising USB devices - but I haven’t yet thought of a way of getting around those. All thoughts welcome!