the reason that your ethnicity isn't "white" is that, for example, if we take the idea that Jews are white, we're completely ignoring the fact that there are in fact many Jews who aren't: mixed-race Ashkenazi Jews, Sephardic and Mizrahi Jews, non-white converts, and many, many others. they're all Jews, but they're not all white: it's a Venn diagram, not a circle.
race and ethnicity are more or less separate; and race is also more or less a tool for the violent destruction of ethnic cultures and the assimilation of them into an unjust, homogenized racial hierarchy.