Stacture WMS can not be displayed from QGIS Data Source Manager

Which means that different styles than default can not be displayed in QGIS using the Data Source Manager -add button is not clickable.

I am assuming that the reason is that something in our Capabilities document is missing or wrong, but have no idea what without investigating more.

GetCapabilities XML request from our service http://3.76.89.1/ows?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetCapabilities getcapabilities.xml

GetCapabilities GetCapabilities response from a GeoServer WMS for comparison (although not with more than 1 style per layer) wms-geoserver.xml

EOxServer GetCapabilities response ows-eoxserver.xml