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

You need to contact your doctor as soon as possible for treatment.  Asking for advice on the Internet will only delay treatment.What you have on your scalp is not normal and needs treatment.

I dislike diagnosing over the internet however you need to immediately speak to a hair restoration professional. This looks pretty angry and could very well be necrosis. This means that the tissue is dying and isn't getting proper circulation. If it is infected this could lead to a worsening condition. Please let us know how it turns out! Take care.

yes that is a superficial skin loss(necrosis) ..5-6 months later you may have a revision surgery and have a small number of transplant to that scarry area to fill the bald field .

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.