TurboCAD Deluxe 20.2
My model has a diagonal line on every facet of simple extrusion and TC surface in hidden line suppress.
I was playing around with walkthrough when I last edited the TCW file.
I have tried CtrlAltW and CtrlW - suggested in earlier posts.
We can offer some guesses, based on what you posted. Such as: Go to the Camera's Hidden Line properties-- right-click on the tea-cup to open that window-- and make sure both Rendering Type and Rendering Mode are set to "Hidden Line"; and in Options/Display, make sure "Draw form building edges" is not ticked.
But it would be a lot faster and more efficient if you could share/upload the drawing file here.
Underneath where you type a post, click on the + sign next to "Attachments and other options". Self-explanatory after that.