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From this answer, (emphasis added by me)

Whether a Jew can cease being Jewish is a controversial topic. In the eyes of the Israeli state it is possible, but probably requires a religious conversion. This was elaborated on in 1962 when the Polish Jew Oswald Rufeisen, who had converted to Catholicism, sought to immigrate to Israel. The Israeli Supreme Court denied his application, arguing that “no one can regard an apostate as belonging to the Jewish people”. Refeisen himself insisted on that he was still a Jew.

I can see that Israel would treat a Jew differently if they converted to another religion. But Jewish Atheism is certainly a thing in the United States and growing,

Overall, about a quarter of U.S. Jewish adults (27%) do not identify with the Jewish religion: They consider themselves to be Jewish ethnically, culturally or by family background and have a Jewish parent or were raised Jewish, but they answer a question about their current religion by describing themselves as atheist, agnostic or “nothing in particular” rather than as Jewish. Among Jewish adults under 30, four-in-ten describe themselves this way. – Pew: Jewish Americans in 2020

Is it likely that a Jew that owns his atheism would be viewed as an apostate by the Israeli Supreme Court, or do they just reject Jews that have converted to Catholicism?