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-...
I'm also unsure if this move would be seen well domestically. They have enough problems right now, and focusing resources on this doesn't sound like it would be met with high praise.
They would simply be stepping into the role on the world stage the US and other Western countries have fulfilled for the last few decades. Israel probably wouldn't be foolish enough to attack them, and their allies definitely wouldn't aid them.
And in the unlikely event Israel does attack their humanitarian convoy, it would only give China an opportunity to do some live-fire practice and score extra points on the world stage as the innocent defender.