Can hairdrying cause and damage on nose after a septorhinoplasty?

No, I do not think that hard drying should have any effect on the nose. Best of luck with your results.

The blow dryer should not impact the result of your rhinoplasty.  The heat may cause some temporary swelling just as may occur with exercise but this will resolve.

Expelled air from a hair dryer is of such minor force that damage to a surgeon's work is unlikely at any stage post rhinoplasty surgery.  Furthermore, at 3 weeks post septorhinoplasty, the dissected skeletal framework has already started to mend where damage to your nose would most certainly would be accompanied with significant pain and swelling.