Anyone can set up a "tribunal" to come to whatever predetermined conclusion they want. This "tribunal" was set up by a literal US-government-backed Uyghur separatist group (the US government is very good at setting up of these sorts of "government-in-exile" groups for countries it doesn't like, like the former "Iraqi National Council"). The chair of the "tribunal" was previously chair of the Falun Gong cult's "tribunal" on organ harvesting. The tribunal admitted that it couldn't find evidence of mass killing, but still decided that it was a genocide, as absurd as that is, because that was the predetermined conclusion the "tribunal" was created to affirm.
This is how the propaganda game is played.
Nobody is being killed, and killing people is pretty much the some qua non of genocide. Anyone can throw around "genocide" as a rhetorical trick. The US killed hundreds of thousands of people in Iraq - genocide? US sanctions against Afghanistan are causing widespread hunger - genocide? Of course not, because genocide actually means something, and we shouldn't hollow out the word to score geopolitical points.
What's happening in Xinjiang? The Chinese government is using police-state methods to destroy the Uyghur separatist movement and to go after religious extremism that it thinks endangers the state and society. The government is certainly violating a great many people's civil rights and dragging up people with only vague connections to the separatist movement or religious extremism. At the same time, the government is pouring money into the region in order to try to raise living standards, on the theory that that will dry up support for separatism and religious extremism in the Uyghur population. As a result, incomes and life expectancy among Uyghurs are increasing. The Uyghur population is also increasing.
There's a real "there" there, but it has nothing to do with genocide, and calling it "genocide" is frankly just propaganda.
To those claiming that this somehow meets the technical UN definition of "genocide," this is simply untrue: the definition requires a deliberate attempt to physically annihilate (not culturally assimilate) an ethnic group. Historically, this has always been through mass killing. The definition says that attempting to annihilate a population by completely stopping any member of the group from giving birth would be genocide, but nothing of the sort is being alleged. The Chinese government has a 3-child policy, and the Uyghur population continues to grow, in fact.