Historical evidence for a separate Jewish branch of Christianity? I've met some non-Hebrew people who have come from a Protestant background, become fed up with their faith, changed churches, etc and now call themselves Messianic Jews. This comes with some claims of things like


They are the true church.
Messianic Judaism developed in parallel with Christianity.
Messianic Judaism is somehow "more authentic" than the Christian church.


What I'm interested to know is this: what type of historical evidence is there to support the claim that the church of the Holy Apostle James in Jerusalem was populated only by gentiles and the "Messianic Jews" maintained their own, separate congregation? Or that this happened anywhere else?

I know Scripture records that the Apostle Peter started doing something like this to a small degree and was rebuked by St. Paul but that seems to support the opposite conclusion.
After Paul's death, Christianity emerged as a separate religion, and Pauline Christianity emerged as the dominant form of Christianity, especially after Paul, James and the other apostles agreed on a compromise set of requirements.[Acts 15] Some Christians continued to adhere to aspects of Jewish law, but they were few in number and often considered heretics by the Church. One example is the Ebionites, who seem to have denied the virgin birth of Jesus, the physical Resurrection of Jesus, and most of the books that were later canonized as the New Testament. For example, the Ethiopian Orthodox still continue Old Testament practices such as the Sabbath. As late as the 4th century Church Father John Chrysostom complained that some Christians were still attending Jewish synagogues.
https://en.wikipedia.org/wiki/Christianity_and_antisemitism

I also remember reading a work of Augustine which mentioned that Christians were still meeting in the synagogue with Jews on the Sabbath. There would be groups like the Ebionites (which may have been heretical) or Nazarenes/Netzrim which were Jewish converts who still kept the law. I would say this separation didn't become definitive until Judaism enacted a curse against them in the liturgy.

Eusebius relates a tradition, probably based on Aristo of Pella, that the early Christians left Jerusalem just prior to the war and fled to Pella beyond the Jordan River, but does not connect this with Ebionites.[11][13] They were led by Simeon of Jerusalem (d. 107) and during the Second Jewish-Roman War of 115–117, they were persecuted by the Jewish followers of Bar Kochba for refusing to recognize his messianic claims.[28]

The 12th-century Muslim historian Muhammad al-Shahrastani mentions Jews living in nearby Medina and Hejaz who accepted Jesus as a prophetic figure and followed traditional Judaism, rejecting mainstream Christian views.[34] Some scholars argue that they contributed to the development of the Islamic view of Jesus due to exchanges of Ebionite remnants with the first Muslims.[13][35]  https://en.wikipedia.org/wiki/Ebionites