It is optional to report your race. That means you have the rights not to report it. When you exercise your rights, universities have to respect your choice; otherwise, they should make it mandatory.
My S is an Asian American and he did not check the box. Among his Asian American friends at Yale, quite a few of them did not check that box. On the official Yale student profile report, they fall into the category of “race unreported,” and not in the category of “Asian American.” 19.1% of 2020 class were “self-reported” as Asian American. Go figure!