Yes, sex matters, that’s why they ask about it at the doctors office. You yourself make the point we can’t erase biology, that’s totally true, that’s why they ask about it.
The reason the say “sex assigned at birth” instead of sex, is because sex is actually more complex than just chromosomes. There are indeed people born with chromosomes other than xy or xx, like xxy, or other things. Some people are intersex. But at birth, even intersex people are usually classified somehow to either male and female, even if their chromosome aren’t that that black and white. So that’s why there’s assigned a birth and not just sex. No one is erasing biology here, they’re just being specific. The sex doctors gave you at birth.
Would it be less offensive if the forms asked about your genitalia? (Do you have penis or vagina or others?) would you be more comfortable if the forms asked about your chromosomes (xy, xx, or others). It’s asking about your biological sex, using very specific criteria (what doctors classified your sex as). For cis people like you and me, it’s very straight forward. But for intersex and trans people, the additional qualifier of “assigned at birth” helps clarify. Just leave it alone, stop freaking out because an accommodation you don’t need is being offered. This doesn’t harm you, but it helps so many others.