There is no evidence that Einstein “became Jewish” or converted to Judaism in order to be “caught by the Nazis.” Furthermore, there is no reason to think that he, or anyone else, would actually want to do so.
All of the evidence shows us that Einstein’s family was Jewish. There is no evidence that Einstein converted to Judaism. Moreover, it does not seem at all logical to think that Einstein did convert. He was a secular Jew, which means that he did not practice Jewish religious rituals or observe Jewish religious law. It makes no sense that someone would convert to Judaism and then not follow Jewish teachings.
Additionally, it is very difficult to imagine anyone would have wanted to be “caught by the Nazis.” Because Einstein was Jewish, he was forced to leave his homeland. He lost his job (though he easily found another in the United States) and had his property confiscated when the Nazis came to power in 1933. (Luckily for Einstein, he was already in the US at that time.) It is inconceivable that someone would voluntarily change their religion specifically in order to be persecuted.
There is no reason to believe Albert Einstein converted to Judaism for any reason, let alone that he did so in order to be persecuted by the Nazis.