Syria is a trap for Americans. Russia, Iran, China have set it up for Americans. Its US' choice to either walk into it or leave
From China's perspective, whatever choice the US makes, it will be a win.
The Saudi - Iran deal has minimised Iran's strategic and military pressure which allows it to refocus to its real target.
I am also that China is also more than happy rhat Iran is now switching its target to US instead of KSA.
The only danger is if Biden decides to flip the tables, but that would overstretch the American Empire, so I doubt Biden would go for that