The truth is that there is nothing substantive that China could do and in fact, the small amount China could do would actually make the situation worse.

Currently, the only thing holding back the West from being completely rabid mask off in their support for Israel (like the EU reversing the aid ban) is because it would completely alienate the Arab world, which they started to care about once again due to their fear that the people they've bombed for three decades would now side with China. This conflict being currently seen as an Israel vs. Arab/Muslim world confrontation is the only thing restraining the West and preventing their anti-Palestinian propaganda from really reaching the Global South.

If China fully sides with Palestine, they'd be able to claim the Palestinians are just Chinese puppets (they recently tried this already by claiming Palestine is just an Iranian lackey) and that'll allow them to push propaganda that this (and all the atrocities they're abetting) isn't an anti-Muslim thing, this is just another part of confronting China (they might even claim "saving the real Palestine from the Chinese influence controlling it").

Another thing is that adding China into the mix and letting the West reframe this with their old Cold War rhetoric would eliminate the substantive progress Gaza's sacrifice has bought on the world stage. One important thing that hasn't been recognized is that the material outcome of Gaza's uprising is that it has been a massive blow against Saudi normalization efforts with Israel. The enemy of the Palestinian cause isn't just the West and Israel, but also the sellout Muslim states like Saudi Arabia, who has basically outright revealed in the past month that they'd happily abandon Palestine if it meant the US would reward them with an expanded military pact and nuclear energy development.

MBS doesn't give a fig about Palestinian suffering and he actually threw Palestine under the bus right before the uprising. Just this month, there was a rumor in the Western press that the Saudis wanted to pause the normalization talks due to Israel's refusal to give concessions for Palestine and MBS was so desperate for normalization that he literally personally went on an US interview to deny the rumor. However, his dilemma is that he has to pretend to care about Palestine because the Saudi reputation as the "Custodian of the Two Holy Mosques" and the "leader" of the Islamic world is contingent on appearing to defend Palestine. Part of the consequence for this uprising is ruining the Saudi attempt at treachery. If the Saudis managed to normalize with Israel, the Palestinian movement is effectively over, because a domino effect would take place. Undoubtedly, the other Gulf monarchies like Qatar, Oman and Kuwait are waiting in the wings for the Saudis to act as the windbreaker to justify their own normalization with Israel. Gaza's uprising brought all of that to a halt and here as well, if China intervened, US propaganda that Palestine was just acting on Chinese orders would give MBS plausible deniability to resume his normalization goals.