I never understood his appeal, but he is extremely popular among the younger crowd on YouTube and TikTok. He is a bit funny and outrageous.
I also seriously doubt people in China know him, given you need a VPN to watch YouTube. I might be wrong though, if his videos are re-posted on Chinese media. They actuallly might think he is another celebrity like Kobe just because he is black.
Every kid knows how to use a VPN. At least the guys, because they need it to watch porn and hentai.
I saw on either Twitter or Reddit (I know, I know), from an American expat teaching English in Shanghai, that every one of his 11th and 12th grade students knew iShowSpeed and that he was coming to China.