If you're going to be a 3D program, basic UV mapping for ALL objects is a fundamental principle. This is a head-smacking-the-wall level of omission here.
I got here because you can't make a 2D extrusion and have it show up as a filled object in plan unless you make it a symbol and add 2D representation (who has time for all that?). Ok, fine let's do a slab instead. Whoops, you can't do UV on it for your 3D renderings. Go back to start. You're being asked to run around the block to get to the front door. Why is this so complicated?