We don’t know how pterosaurs evolved powered flight. The most primitive, probable, ancestor of pterosaurs had a bodyplan closer to that of a kangaroo. And the earliest pterosaurs like Preondactylus or Eudimorphodon were already fully capable of flight.
No evidence if the intermediate species. It makes sense, but without evidence, it’s just conjecture.
And with gaps in fossil record that last for millions of years, who knows whether we will ever figure out the pathway to flight.