If the census is "mandatory" where you are, demand the paper form. Then you can refuse to answer / do other nonsense for any question you don't like. I quit out of the online version the moment it validate-shamed me and demanded I comply with its restrictions
I did this last time, drawing a line through every question that I thought exceeded the original scope of the census here (which is pretty much all but one of them). I got a couple of semi-nasty phone calls from a supervisor of some sort trying to get me to answer the questions, but I stuck to my guns.
It's theoretically possible to get fined here for refusal to complete the census, but nothing happened to me. I'm guessing it's similar in most western nations.