Most of those 400 million people never existed since thei existance was in numbers on a spreadsheet only.

How come all these populated areas are now deserted?

I would approach this question as cautiously as I approached "How come everyone in China are dropping dead on the streets" during 2020. Remember all those videos we were watching? Yeah, its all a psyop. Everything is a psyop.

Instead of answering as to how exactly the psyop is being spun, its far better to focus on what the goal of the psyop is.

When it comes to China, there are two psyops - the benign WH psyop to ease the economic realities of China to the world, and the CCP psyop to try and delay the inevitable and portray US/Trump as the villains.

My whole YouTube feed is filled with China related videos - and everyone is refreshingly original I have to say, even though most are complete rubbish. A lot of these people are becoming part of these psyops purely by their own emotions behind their strong held beliefs about China - be it China-loving or China-hating - I get both in equal parts, and both side are completely missing the real picture. Its very funny actually.