Embedding vector of MaskRCNN (Resnet with FPN)

I have a MaskRCNN model for instance segmentation with Resnet 50 - FPN backbone implemented trained in detectron2. And I want to extract the embedding/feature vectors for visualising input and hopefully detecting outliers. Which place would be the best to extract the the embedding vector? I tried p5 of FPN which shape is (1,256,51,68), but it's a tensor should I flatten this and feed into visualiser?

computervision detectron2 embedding extract feature outliers resnet segmentation vector vectors