Hello. I bumped into this topic lately too, in a book titled “Elohim; They Are God” by Ben Shlomo, a Jewish Christian and ancient Hebrew scholar. He asserts that the Jews were believers in the Trinity, but like many Christians to-day, were not clear exactly what that was, or who they were, if you prefer. An interesting idea and book.
Before dismissing this idea out of hand, consider this. In the New Testament, as far as I recall, Jesus was confronted for claiming to be
God’s son, not for claiming that God had a son. There is no controversy over the Great commission, “baptizing them in the name of the Father, and the Son, and the Holy Spirit”. There is no controversy in Acts or the epistles over references to the Father and/or the Son and/or the Holy Spirit.
If the Shema were as central to Jewish belief in Jesus’ day as it is to-day, and understood then as it is to-day, one would, I think, expect at least some controversy about the Three in One God. But the Bible records only disputes about circumcision, meats, days and laws, etc.
Shlomo mentions the date of about 200A.D. as the time when Jewish leaders started downplaying belief in a three in one God and emphasizing the Shema as meaning one God with no Son.
I am not qualified to comment further about this topic, but it does seem to me to be possible.