From reading the posts here, it sounds as though very few of the respondents have actually participated in a Census or have a clue as to what is asked.
The Census is taken every 10 years, with 2020 being the next.
It is designed to be answered be all residents of the US, it's possessions and territories, with a claimed 99% penetration rate.
There are generally 2 Census forms, a long form and short form, which are sent at random.
Short forms at usually 8-10 questions, while long forms are 30-80 questions.
Some years only 1 of those forms are sent, 2010 was such a year and only short forms were sent out, indicating that 2020 will most probably see both long and short forms sent out once again.
The American Community Survey is done yearly to collect additional data to supplement the Census. It has a designed penetration of 1 in 6.
Asking about citizenship is
not a new question, and has been on the Census before, notably without objections.
https://www.npr.org/2018/03/27/597436512/fact-check-has-citizenship-been-a-standard-census-question
And for those that think it is an intrusive question, here are the Census and ACS questions from recent surveys.
https://www.census.gov/history/www/through_the_decades/index_of_questions/2010.html
https://www2.census.gov/programs-surveys/acs/methodology/questionnaires/2017/quest17.pdf