Pornography is not banned in China. Selling, purchasing, transporting, or producing it for PROFIT is banned. If you want to draw or write some smut and put it on an 18+ forum, no one cares or is going to stop that. Self made porn is also not banned if you aren't disseminating it for profit (something like Onlyfans). Artistic, educational, and medical depictions also have exemptions under Chinese law, and a lot of drawn pornography sites use the artistic exemption.

If you make a website selling pornographic art or films or open a film studio, that'll get taken down and is very illegal. For example the site Erotica Juneday required users pay around 20-500 dollars a year for their service. That was taken down and the administrators were imprisoned. The Chinese version of DeviantArt and Rule34 however are free and run no advertisements, and they have remained up for years.

Peer to peer dissemination is also not illegal, which is why services like Baidu offer that as a service.

Further, the vast majority of Chinese people use VPN's, and it is estimated that a large percentage of that traffic is to foreign pornographic sites.