What is the "censorship" situation like in China?

I understand the Great Firewall, non-chinese websites can't be accessed without a VPN. But, like, is it true that you aren't allowed to criticize the government? Is it illegal to do so? Like do you go to jail for it? Or do you just get banned from the social media app you posted it on? Or does it work in a different way? And what about all the "spy cameras"? How do those work? I've sorta become hyperfixated on China recently due to Xiaohongsu and TikTok and I've been unlearning all the anti-China propaganda the US government has fed us. I wanna learn the truth about this great nation.