Forced sterilisations have unfortunately happened all over China as a result of the One Child policy. To my knowledge that has occurred across the board and no ethnic group was ever specifically targeted. In fact under the One Child policy minorities have the right to have more children than the Han majority, and they do have more children. So reporting that "some forced sterilisations" have occurred is not really significant in itself.
Likewise, when it said that the birth rate has significantly dropped I think it would be useful to see figures (if they exist) on the average number of children per woman in the region because, again, China has a pretty strict birth control national policy and that would allow to see how it was enforced in Xinjiang before versus now.
The figures quoted in an article I quickly found through Google [1] suggest that the One Child policy (even with recent relaxation) was not strictly enforced and that the birth rate was much higher than it should have been under national policy. If so that could mean that they were cut some slack and have now been brought in line with the rest of the country. Of course this is from the Golbal Times, an official Chinese organisation, so I do not know how reliable the figures are.
[1] https://www.globaltimes.cn/page/202101/1212073.shtml