996 means 12 hours a day 6 days a week. It's something that's becoming increasingly common in white collar jobs in China and this video which I find extremely accurate as I could see years ago this was how things were going to go.
It's bad leadership combined with always connected to employee smartphones that has escalated this. This idea that the longer hours you work the more will be achieved does not work in an office environment. If you were paid to lift bricks, sure the longer time you spend lifting bricks the more bricks you'll move. But in an office environment it does not work like that, unless you are say for example a low level data entry position.
I've worked in a few Chinese companies and back in the early 2000's it was typical for office workers to work six days week, 40 hours and maybe a couple of hours overtime. Then you went home, the boss would not call you and most people did not have internet access outside of the office.
10 years later I had an extremely well paid job but the boss wanted all my time. Public holidays? - Come to the office, let's have a meeting while it's quiet. An idea pops into his head at the end of the day? - Here, finish this presentation for tomorrow mornings client meeting (Several hours worth of work). I had to actually take some time off because of burnout. I worked out he only did that becuse he lived alone and had nothing to do during the weekends and holidays as his family lived in America. It was bullshit busywork becuse he was bored.
I had another boss who would always make a show of how hard he was working but it was bullshit. He'd claim to be working to 11PM each night. But the reality as I observed was he'd often leave the office at 5-6 and go out eating or drinking for the evening. Then when he was about to go to bed fire off some emails from his phone and fall asleep. working until 11pm...
(Actually watch out for this one as I've seen many people just fire off emails late at night to look like they are working really late at night for the company)
This 996 mentality for office workers means they are getting a worse deal than uneducated factory production line workers. At least they are paid by the hour and paid overtime. Not only that but they get food and accommodation and the work they do "Lifting bricks" actuality leads to more productivity for the company.