You can flare power off with 40 flaps provided you have enough airspeed
Yes, though the airplane will slow down very quickly when you raise the nose with more than 20 flap extended. I'm happy to see the flaps extended from 10 to 20 when the runway is "made" power off, and everything is stable, and then selected 20 to full as the flare is begun. If you time it right, it works fine, though this, as said, is best practiced under competent supervision. In a Cessna, a power off approach with more than 20 flap, other than close over the landing surface, is unwise.