In Dolphin, under Places, not all partitions are displayed, only personal folders and basic folders. If I want to add the entry I find under the path / Media no entry.
Where are the places for the partitionen?
Dolphin can only display what is mounted. Did you add those /media partitions to fstab?
If you want to make a custom entry in Dolphin you can right click in the "Places" area and make a custom entry based on the "location" you're pointing at like /media.
Attached storage typically auto generates an entry but if it's a directory path you want in Places you'll need to create it.