You can create a prefab instance by dropping a Prefab file into the scene, dragging it from the Files view or the Blocks view.
When the active editor is a Scene Editor, the Blocks view shows the Asset Pack file items and the Prefab files:
You can open the Prefab file of a prefab instance with the Open Prefab command. You can press the F key or execute the command in the context menu, in the Prefab sub-menu:
The Inspector view shows a section for each prefab (and prefab variant) of the selected objects. In the menu of the section, you can click the Open Prefab option:
