The Bolt is not direct drive, it has a single motor hooked to a fixed gear ratio final drive and a differential in it. It looks like Chevy doesn't actually provide a maintenance schedule for the oil in the gearbox but it's no different than any other gearbox, the oil will wear down from shearing and contamination will build up over time. 100,000 miles is probably a good service interval but Chevy doesn't bother to tell you how often you should change it.