Social media
Oh no, we understand that this one would be an absolute nightmare for so many people who are addicted to all kinds of social media these days. While China has some social media they allow and heavily monitor and regulate, they have banned many others from being used in their country.
We can understand that they do not want any information spreading from the outside world into their own country and infecting the minds of their citizens. Especially if those ideas created public unrest and threatened the power of the political institutions. Communication is key for people to spread ideas and organize, so no wonder it’s banned.