The Supreme People's Court didn't deem "996" illegal in 2021, it was illegal all along, what it actually did is include examples of "996" in a list of typical labor disputes: (Chinese article) 2021-08-26 https://www.court.gov.cn/zixun-xiangqing-319151.html. The actual government entities handling the cases were local "Labor Dispute Arbitration Committees", some went to court.
996 is definitely still a thing, I don't know how widespread it is, but it'll probably still be around for a long while.