Hello. Referring to my post in this thread, I would like to note that at the moment we do not have a quick method that allows us to easily animate the smooth effect of changing transparency of objects that have many materials.
In this case, you have to edit the settings and data in each of the materials separately, because as you know you can select only one material slot at a time, so changing the data with the “alt” key is not an option.
And that’s why I would like to suggest creating an addon that would make it much easier.
Principle of operation:
In each of the materials assigned to the selected object, after clicking the “Add” button, addon should add “Transparent BSDF” and “Mix Shader”, in which the “Fac” slider will be controlled by a driver whose value will be determined by the user on the panel. There may be a dot next to the slider that lets you easily add key frames.
The panel also contains standard material settings used by EEVEE, editing of which should also affect all materials in the selected object.
Additionally, after clicking “Add” they should be set automatically as shown in the graphic below.
The “Remove” button removes any changes made to all materials at once.
What do you think about this idea?