TLDR
The US is butthurt that China’s economic growth and influence (Belt and Road projects) are increasing, so they partnered with Western nations to go on a propaganda spree against China with their issues, e.g., Hong Kong, Taiwan, and Xinjiang.
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Why Xinjiang?
1. The majority of the population are Muslims, which makes them the minority in the country. Sounds at a disadvantage, but a lot of people don't know that ethnic minorities in China have priority (lower entry requirements in education, etc) and special privileges (more than one child, etc) allocated by the government.

1. There were terrorist groups and activities in the past, which China has mostly controlled by tightening its borders and increasing surveillance throughout the country (why censorship and profiling exist today). There were also internment camps in Xinjiang where people involved in terrorist activities are trained and then released (note that every country has its version of these camps, such as the Rohingya Camps in Malaysia).

US Involvement
The US see this as an opportunity to destabilise Xinjiang and give China a bad rep by claiming that Uighurs are oppressed, and called it human rights abuses. They came up with these allegations:-
a. Concentration Camps
Claiming that Uighurs are kept in camps with random satellite images of
buildings.
b. Genocide
Claiming that Uighurs were sterilized by using a few women to testify.
c. Forced Labour
Claiming that Uighurs are forced to pick cotton when all of them use modern
machinery to harvest.

The forced labour allegation took off with Western firms boycotting cotton from Xinjiang, but diligent companies like Skechers took the initiative to visit unannounced and found no abuses (statement on their website). There is also an increasing number of Western and Muslim vloggers debunking the allegations on YouTube.

Until now, there is no credible evidence to back the allegations and news just keeps spreading as people only read headlines.

I am not saying that those allegations are not real; what do we know? The media are all controlled (our country is a good example) and we should not just take in information blindly.

Western nations always have their interest in being the dominant country and will try to drag developing countries down. Right now, the US is actively politicising the origins of Covid-19 being from Wuhan, which scientists have rebuked while investigations are still ongoing.