Does one have to be ethically Jewish to be a humanistic Jew?/ I’m tryna learn more about Humanstic Judism

I’ve been trying to research going to different branches of Judaism and humanistic is apparently one that’s less focused on the theistic aspects of Judaism and more on the cultural. So it got me thinking, does it follow the standard to be a Jew your mother has to be Jewish thing or could somebody who is not ethnically Jewish become a humanistic jew? I can’t seem to find a straight answer online.