On all of my other recent models the faces were default white/blue with black lines on every edges.
On my current model, when I began to extrude faces the style became more presentational, so that my edges were only visible when against the background.
I have played with the style and layer options but it has not brought the lines back.
What version of SketchUp are you using? Your profile provides conflicting information. If you are using SketchUp 2018, it must be Pro. If you are using Make, it must be 2017 or earlier. Perhaps you could correct your profile info.