GeoServer & QGIS - Using GeoJSON in a WFS request

I'm trying to load a WFS Layer in QGIS. I requst the data from my GeoServer and would like to import the data as GeoJSON.

I can export my data in the layer preview section as GeoJSON. Everything works fine.

But i am unable to display my data in QGIS. I tried to add the "&outputFormat=application%2Fjson" at the GetFeature request.

I think my issue belongs to this similar question but the author did not answer the question of @nmtoken if the WFS GetCapabilities request for the service is listed GeoJSON as a GetFeature ResultFormat. In my case, the format is listed.

Here is the output of the GetCapabilities request:

   .
   .
   
     
      application/gml+xml; version=3.2
      GML2
      KML
      SHAPE-ZIP

      application/json
      application/vnd.google-earth.kml xml
      application/vnd.google-earth.kml+xml
      csv
      gml3
      gml32
      json
      text/xml; subtype=gml/2.1.2
      text/xml; subtype=gml/3.1.1
      text/xml; subtype=gml/3.2

     
   
   .
   .

Please give me a helping hand here, maybe it's not possible to load my data as GeoJSON through a WFS because it will always provide the data as XML? I tested it with WFS 1.0.0, 1.1.0 and 2.0.0

Versions:

QGIS 3.2. 
GeoServer 2.12.1