Some time ago, I used to talk to a guy who’s Brazilian Israeli. I remember he was only 1/4 Jewish and didn’t know much about Judaism. When he became interested in Orthodox Judaism here, he couldn’t take part in it because he wasn’t Jewish by halakha. Many such cases
He’s a Spanish Sephardic Jew, and his family is from Turkey and Greece. If I’m not wrong he was involved with a Masorti congregation here