The renaming of material areas takes place in the Layout Editor. This can be opened in the first step.
The view looks as follows:
Now first select the option "Layout movable". This allows you to move and edit areas in the layout.
The next step is to select an area. This is done by clicking on any area. Here a small window opens in which different parameters of the selected area can be seen, including the name of the selected area.
In the next step, change the name and confirm the entry with Enter.
The newly defined name for the material area is then used in the 2D view and in the 3D view.