Gaza has a sizable coastline, and China has a large number of amphibious assault ships available. They can defend themselves against Israel air attacks. If China decides to send humanitarian relief to Gaza, China can do it, and Israel can't stop them.[3] China would look like the good guys. Which their leadership knows.
[1] https://www.foreignaffairs.com/china/chinas-game-gaza
[2] https://edition.cnn.com/middleeast/live-news/israel-hamas-wa...
[3] https://www.newsweek.com/china-amphibious-assault-ship-type-...
The line of thinking is that if Israel is subject to international courts/laws regarding genocide for its action, then China will be too. China's participation in judging Israel opens itself to the same judgement.
1. https://en.wikipedia.org/wiki/Uyghur_genocide
2. https://en.wikipedia.org/wiki/Territorial_disputes_in_the_So...
I don't see folks buying that, sorry. In international realpolitik you play the cards you have and if your rival opens themselves up for criticism you play it.
Rhetoric trumps logic in this one.