That's not at all true. The citizenship question was removed from the 2020 Decennial Census by the Supreme Court in Department of Commerce v New York (2019) which held the Department of Commerce failed to provide a genuine justification for the decision to add the citizenship question (as required by the Administrative Procedure Act), instead providing a contrived and pretextual explanation.
That was the administrative reason why the question was not permitted. The case was raised to begin with because of fears it would result in undercounting non-citizens, who would be less likely to respond because the don’t trust that the data would remain private. This explanation is outlined in the section called “2020 Census” in the Wikipedia article you linked.
https://en.wikipedia.org/wiki/Department_of_Commerce_v._New_...