2007 Subaru Outback revving too much with no power

It certainly sounds that way. The clutch’s job is to join the engine to the gearbox while still being able to disconnect them when you need to idle the car or change gears. If the clutch is worn out, you’ll find it slipping under load, allowing the revs to flare up and the vehicle not moving much. This sounds exactly like what you’re describing.

At the least, you’ll need a new clutch unit, but if it’s been slipping for some time, there’s a chance the flywheel has been damaged and will also need to be replaced or machined. I’m tipping that when you tried to reverse out of your parking spot most recently and revved the engine out with no motion from the rest of the car, there was a terrible smell a bit like the smell of brakes in a railway station when a rain pulls in. If so, that’s a clutch failure for sure.