AHC: A synchronistic Islam/Jewish religion in 20th century

What if during a Nazi victory the Nazis begin to attack amd exterminate the Middle East since they are Semitic. Using the map from Phillip K. Dicks "Man in the High Castle" lets assume the Slavic people, Jews, amd other who were able to escape extermination were able to resettle in parts of Siberia and Kazahkstan. In this timeline the Muslims who were not exterminated also go to these areas. There a young man of Jewish descent listened to a Rabbi and went and prayed, he had a vision and began to preach unity between Jews and Muslims. Slowly there are followers who soon joined this fringe group. Boris Belikov received a vision that the sons of Noah needed to unite and become one in worship. Imams and rabbis soon distanced themselves from this charismatic leader but he became a pillar of the community. He opened soup kitchens, clothing recycling for widows, orphans, and the invalids. The Religion known as Sons Of Noah became small but powerful. Boris taught that Islam and Judaism are the same because Muhammad was a relative of Noah thus proving his prophethood amd converting Jews and Muslims in record numbers. The Sons of Noah celebrated the Jewish and Muslim holidays, reincorporating Polygamy into Judaism and keeping with Islam but the major difference was that Belikov preached that cousin marriage was not okay according to the laws of the Semitic people's. The major languages of Hebrew, Arabic, Russian, Ukrainian and many others became common in Siberia and Kazakhstan. The Sons of Noah became known not as Jews or Muslims but referred to themselves as Semites. The Jews and Muslims became a group the Nazis soon hated. Many formed militias, Muslims having fought the British and later Germans while the Jews were familiar in combat from their battles in Stalingrad the Jewish uprising and other conflicts. Feel free to add on
This isn’t really an AHC, as you already gave the scenario.

This scenario relies on a faulty understanding of Nazi ideology and antisemitism in general. Antisemitism has nothing to do with a so-called Semitic race, as “Semites” are not a racial group, but rather a language family. Racists have used linguistic evidence to come up with “races” before, most infamously the use of the Indo-European language family to come up with the concept of Aryans. However, 19th century racists never posited a Semitic race including Arabs. Antisemitism was just a word coined to make Judenhass (Jew-hatred) sound “scientific.” The misuse of “antisemitism” to mean Islamophobia is now a common antisemitic trope (eg. Helen Thomas and Roger Waters). It allows them to deflect claims of antisemitism by talking about Arabs. They also often say that Israelis are the real antisemites because of their treatment of Palestinians, which is just a transparent attempt to erase hatred of Jews. I think the word antisemitism should be replaced, but I don’t think it will happen.

Also, even if Nazis believed in a Semitic race, why would they kill all Muslims and not just Arabs? Nazis considered Berbers to be Aryan, and Azeris, Albanians, and Bosniak Muslims would also be considered ok by the Nazis. This is leaving out Iranians, Indonesians and sub-Saharan African Muslims as I don’t know what Nazis thought about them.
Also, in the Biblical and Quranic narratives everyone is a descendant of Noah, so arguing that Mohammed is would be tautological.

Interestingly a minuscule Noahidist movement actually exists today, but there’s no connection with Islam.

Sabbateanism is a good example of real syncretism with Islam.

Many Rabbinic Jewish scholars were influenced by Islamic thinkers, for example Maimonides was heavily influenced by Averroes.