You mean, a shadow cast by a building onto a cloud? That seems like the most plausible explanation, but if that's the case, why isn't it a constant feature, why is it only appearing now? Also, it looks more sharply defined than I would expect if that were the case.

> why is it only appearing now?

Maybe the clouds have to be just the right height/composition to see the effect. If the clouds were higher it might be too small and diffuse to see, maybe the lower clouds are partially blocking some other light sources making it much more pronounced or something along those lines.

Why did no one break out a high powered laser pointer or range finder?

I feel that if it was cast from a building, the shadow would be stretched down to the source. However maybe a shadow from some kind of kite?

Appears not, it can clearly be seen above the cloud or smog, this sped up video shows this to be the case: https://www.reddit.com/r/UFOs/comments/o5r4hw/sped_up_shangh...

A shadow cast at a distance has blurry edges. Those are crisp. Also, there are clouds that pass in front. I wonder if 1+ drones are creating this visual