How to make an object (triangle) transparent inside leaving angles highlighted? I am new to Blender but have done a couple of tutorials already. Now I wonder how can I select the angles of a triangle and fill the content of a triangle with black. Or maybe there is an option to clear this content and leave it fully transparent? I have attached a screenshot to get a better understanding of what I want. Thanks in Advance! :)
You could mark the edges as Freestyle. You have options: in EEVEE, you can render the layer on its own, by unchecking all other passes in the View Layer Properties tab, or in Cycles, as illustrated here, you can check 'As Render Pass'.
In this example, 'Film' is set to 'Transparent' in the Rendering tab, and the Freestlyle layer is laid over an Input&gt;RGB node  black in the compositor.

(Blender 2.92)