My "Mix Shader" node doesn't have a "Fac" input socket I have seen some videos, but I noticed that there is a problem, is there no &quot;fac&quot; command on Mix Shaders?

i can't find it... (blender is in italian: &quot;somma ombreggiature&quot; ==&gt; &quot;mix shaders&quot;)
There is a Mix Shader node with a fac input and an Add Shader node with only 2 shader inputs, they are not the same node :

Or in Italian