Originally there were "tie down hooks" there which really were plastic grocery bag holders. If you have the rear cargo cover, it connects to these.Looking at that first picture makes me wonder if I am missing anything that can screw on to the four holes.
"Tie Down Hook": 6426735020B0 or 64267-35020-B0
"Screw with washer": 90159-60411
From the owners manual: