Thanks, now I get it, it’s super easy and I see first results as the rendering is slowly updating.
I’ve been adding a lot of pipelines, storage tanks, bunkers and ruins to industrial areas and apparently all of these features are assumed to be underground if not tagged otherwise. And it makes sense to not render underground stuff except maybe an icon like for bunkers and storage tanks. I’m going back updating the stuff I added, cause creating holes into enclosing landuse areas makes that area consist of a mess of lines within it instead of one clean outline. Of course I’m not going to use the tags to now make everything render above ground, what is above ground goes there, what is below goes below. It makes so much sense to render just a storage tank icon if it’s underground and if you really want you could still look up the shape below the ground.