“Does sitting cross-legged stretch hip flexors?”

Yes this will stretch the hip flexors a little. The psoas muscle, rectus and sartorial will get some stretch. Hip external rotators will get more. Look up specific stretches for muscles mentioned on utube or google for more specifics. Many yoga poses are good for this. Good luck.

No, that stretches the hip abductors. To stretch the flexors, lie on your stomach on the floor. Keeping your pelvis on the floor, lift your upper body with your arms. This will extend the hip joint and will stretch the hip flexors.
Hope it helps!!

Dr. Bose