Blackout 3D Cone of vision/Line of sight

Hello everyone!

So I'm working on a 3D top down game and I want to essentially have a cone of vision of what the player can see. With everything in that being seen and anything not being blacked out entirely.

And I'm not entirely sure where to even begin here, a lot of stuff on this tends to be in 2D. Which isn't great when somebody can be up on say a balcony thus be unseen by the railing et cetera.

So far the closest thing I have found to what I want in terms of sight alone would be the commandos cone of sight. (Link here: https://github.com/joscanper/unity_coneofsightfx ) but if I said I have no idea what I'm looking at then I wouldn't even be scratching the surface of my ignorance.

I mean this is great! But I have no idea how to use it (get stuff that is seen. Its very different to raycasts) for example blacking out everything that's not seen.

Thanks for reading.