Basal Euparaves could fly by flapping their wings, but they lacked the muscle structure to take off from the ground. In other words, they could fly but they were not capable of "powered flight".
Some of the literature gives the impression that they could only glide and parachute.
But they could fly. They just were not capable of "powered flight" (they could not take off from the ground).
And basal Euparaves could fly even though they did not have asymmetric feathers.
This is all very important because the dinosaur to bird theory is built on the idea that basal Euparaves could not fly.