Double rod mesh including privacy screen on L-stones! Feasible?

No, that was not discouraged. It was discouraged to screw the fence onto the top of the L-bricks because there is simply very little "material" there. Screwing from the back could also work, but you must absolutely not drill too deep ;) And better one screw too many than too few.

So in my original post, I did write that I ordered the L-brackets for the L-bricks. These can only be screwed from the back or with just one screw from the top. I assumed that this variant was discouraged.

This is what the holders look like. That would of course be much easier. But as long as there is a risk that it will come loose, I would rather use concrete.

How much distance does the hole have to the edge? I would be very careful with less than 10cm edge distance, otherwise the anchor will break the concrete.

The top two holes definitely have less. They go in the middle of the L-stone. They are about 5cm. The lower hole is 12cm.

Short update:

You were of course right. The fence on the L-bricks would have been way too high. We have now set it to 1.2m and continuously raised it with the bricks. It fits perfectly and you don’t look at such a high fence. Attached is a picture of our ground. I can only get the rear posts deeper with extreme effort. The hole is 60x50x70 (70 deep but only 50 of that is filled with concrete). But if I put concrete in there, it should solidify with the rocks and then nothing should happen, right? All other posts were concreted with about 200-250kg of concrete. Thanks again