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This would effectively mean that the one we're seeing here is the cast shadow of a building, and that the sky itself is illuminated by the light. The "UFO" is in fact, a shadow

I think this seems like the most reasonable explanation

But when they pan down and back up you can see there's no light show on at that time from the buildings. Also if a light show, the lights are colorful, and often strobing and rotating, but the triangle is static. I think lightshow is debunked.

But it's a fair guess. I also think that a static vertical spotlight atop a building could do this, but the air in Shanghai is not exactly particulate free and if you had these powerful light beams you'd expect to see a trace of them along the line from source to cloud, but there's no such. I think the ground-source idea is, well maybe not debunked but less likely than "odd triangular air mass", or CG. It could be a massive drone or something suspended from helicopters above it, maybe it could be like a light or firework platform that's being tested as part of the centenary celebrations?

So, it must be communist aliens then