incarcerated more than an estimated one million Turkic Muslims
This is estimated based on incarceration rate etc.
Leaked data reviewed by the Associated Press revealed that almost one in 25 people in the Uyghur heartland in western China have been imprisoned on 'terrorism-related charges' - the highest known incarceration rate in the world.
Xinjiang has a population of 25,890,000 based on the last census.
AFAICT the estimates are based on sampling some counties, so it is possible that the extrapolation is not entirely correct (to the rest). YMMV.

I'm a bit but right now, so I didn't read all the details, but this doesn't appear to include those just sent to 're-education'.
The list does not include people with typical criminal charges such as homicide or theft. Rather, it focuses on offenses related to terrorism, religious extremism or vague charges traditionally used against political dissidents, such as “picking quarrels and provoking trouble.” This means the true number of people imprisoned is almost certainly higher.
But even at a conservative estimate, Konasheher county’s imprisonment rate is more than 10 times higher than that of the United States, one of the world’s leading jailers, according to Department of Justice statistics. It’s also more than 30 times higher than for China as a whole, according to state statistics from 2013, the last time such figures were released.
And yeah, China hasn't officially provided any figures for the more informally detained in "vocational facilities", so there's that. But there is some official data on the sudden increase in long-term sentences in 2017, as OHCHR reported
The [Chinese] Government has not released official data about the number of individuals who have undergone re-education in VETCs. In 2018, the UN Committee on the Elimination of Racial Discrimination noted that “estimates of the number of people detained range from tens of thousands to over a million”, and called on the Government to provide statistics for the past five years. In response, the Government asserted that it was not possible to state the number of those taking part in education and training, because it “is dynamic, as people are
continuously coming and going,” a position it has maintained since.
In the absence of officially available data, [...] it has
been estimated that around 10-20 per cent of the adult “ethnic population” in these counties and townships were subjected to some form of detention between 2017 and 2018.
Another change in 2017 was the increase in the number of people given sentences of
five years or longer. Prior to 2017, approximately 10.8 per cent of the total number of people
sentenced in XUAR received sentences of over five years. In 2017, that figure rose to 87 per
cent of the sentences. According to official Government statistics, during 2017 alone, XUAR
courts sentenced 86,655 defendants, or 10 times more than in the previous year, to prison
terms of five years or longer,
although again it is not possible to disaggregate the number
charged and convicted for terrorism or “extremism”-related offences.
And yeah, even that OHCHR report has been much delayed.
TBH, I'm not sure why OHCHR didn't cite these figures (perhaps the very long delay to publication is at fault), but SCMP reported in 2020 that the Xinjiang regional government released some figures on the 'vocational' centers:
Titled “Employment and Labour Rights in Xinjiang”, the white paper said the regional government had organised “employment-oriented training on standard spoken and written Chinese, legal knowledge, general know-how for urban life and labour skills” to improve the structure of the workforce and combat poverty.
It had provided vocational training to an average of 1.29 million urban and rural workers every year from 2014 to 2019, the white paper said, apparently not using the Chinese government’s five-year planning period as the reporting time frame.
Of those workers, about 451,400 were from southern Xinjiang – an area it said struggled with extreme poverty, poor access to education and a lack of job skills because residents were influenced by “extremist thoughts”. That period was also when regional authorities introduced a “systemic de-extremification” campaign to counter terrorism and extreme religious thoughts, according to mainland media reports.
A mainland-based academic who studies Xinjiang issues said it appeared to be the first time Beijing had “indirectly acknowledged” the number of ethnic Muslim minorities receiving “vocational training” under the “de-extremification” programme.
“If you take into account the timing of China’s de-extremification measures that began in 2014, the ‘1.3 million people being trained per year from 2014 to 2019’ is very close to the number [in the camps] estimated by Western critics,” said the academic, who declined to be named because of the sensitivity of the matter.
“But China does not see these training facilities as internment camps, and what it is really trying to highlight [through the white paper] – to counter Western criticism – is that the ‘vocational training’ they provide is actually a social service to improve people’s livelihoods and alleviate poverty.”
Anyhow, the OHCHR report stated that many of those interviewed said they didn't have choice about attending these, amusingly citing apparently the same Xinjiang State Council Whitepaper:
The 2019 White Paper on “Vocational Education and Training in Xinjiang” states that the centres are “residential”, and that referral follows a decision by the court or public security officials, rather than being voluntary. This is the case even for referrals by the procuratorate, where the concerned individual is given a “choice” between referral to a VETC facility and a prison sentence, implying that placement in a VETC is a form of alternative sanction to a prison sentence.
Individuals interviewed by OHCHR who had been placed in VETC facilities described being taken to such facilities, usually by public security officials. The majority of the interviewees who were apprehended between 2017 and 2019 were held at a police station
before referral to a VETC facility. They said that they were told that they had to go to a VETC facility and were not given an alternative option. None of the interviewees felt they could challenge the referral process, and none had access to a lawyer prior to being sent to the VETC facility nor at any point during the time they were present there. Several underwent long interrogations in police stations before their eventual placement.