Don’t they have an APU any longer? That little beanie head propeller thing doesn’t look like it would provide much juice, to be honest.
Yes, they still have APUs, but the APU is not normally running during flight.
The Ram Air Turbine automatically deploys in seconds to provide essential electrical and hydraulic power to keep the aircraft flying while the APU is started, which can be a 30 second to 2 minute process, if it will start at all.