4 weeks post FUE, Is this condition normal sometimes or is it necrosis? (photo)

From the photos it does look like you may have lost some tissue.  This ought to be evaluated in person to assess the extent and depth of the tissue loss, and to provide wound care to prevent infection and worsening.  Go see your surgeon.

The location of the necrosis is where all of the blood vessels end and join up to supply the needed blood flow for the scalp.  Make sure that the doctor who will treat this understands how to manage this rare complication.