srcset, which is what is in your page. https://www.caniuse.com/#search=srcsetobject-fit being used, as that is not totally handled by Edge (https://www.caniuse.com/#search=object-fit), but I didn’t see it in there.
Your page has the huge image referenced, and smaller versions in the srcset. I would have specified the image most likely to be used (the small one), and then the srcset can reference all the larger ones. Why would you ever need that image to be more than 5000 pixels across? It’s a waste of your server disk space to store such huge images plus all the smaller ones that actually might get used.