Constituationally, they’re counting people, not citzens. There’s nothing in the Constitution about counting citizens.
The “Long Form” or American Community Survey does ask about citizenship. It doesn’t ask about legal status.
The count for Congressional districting doesn’t distinguish between citizens and non-citizens - and it never has.
It asks where you are born in question 7, "Where was this person born", and asks for state name, or "outside the US", then Question 8, "Is this person a citizen of the US".
Just filling out this form since this thread reminded me I received it.