from the list of metadata records a mapContextLayer is created by the button "Add to map".
If only one layer references the metadata record, this layer will be linked directly to the mapContextLayer and the corresponding symbol for rendering option see below will be colored / active (see ticket mrmap-community/mrmap-react-frontend#9)
If multiple layers reference this metadata record, only the mapContextLayer is created (without linking to any layer). The icon is grayed out / inactive in this case.