Definitely allies of convenience. China doesn't like Muslims, as evidenced by its treatment of the Uyghers. And I think it would wet itself with delight if it could stand aside while the Europe/USA block and Russia had a serious atomic fight, leaving resource rich, population poor Siberia open to reconquest, and removing all serious rivalries to its hegemony.
CCP loves Muslims and have been allies of PLO since the 70’s at least and every Islamist regime. Pakistan has been their close ally and they gave Pakis the bomb, essentially.
They don’t like East Turkestanis because they rebelled against them.
No Muslim state stands up for the Uighurs.