One thing about the Trinity that is not a mystery is its origins. The doctrine came from the Catholic Church around 381 CE – long after the Gospels were written, which explains why it was unkown to whoever wrote the New Testament. At least that is when it was accepted as doctrine. The Jews never believed in a Trinity, and the church adopted it under pressure from its most pagan segments of the Catholic Church.
IMO, it is a losing battle to try and prove this fourth century doctrine to Jews who follow a monotheistic Torah.
BTW, the word Elohim is also used to refer to Moses (Ex. 7:1). No one, after reading this verse, mistakenly believes Moses was more than one.
For Christian Support that the use of “Elohim” does not refer to a trinity, read the following commentary from the author of the “New INternational Version Study Bible”:
“God created. The Hebrew noun Elohim is plural but the verb is singular, a normal usage in the OT when reference is to the one true God. This use of the plural expresses intensification rather than number and has been called the plural of majesty, or of potentiality.” (p. 6.)
There’s more explanation, but this should cover it.
For more detail, outreachjudaism.org/nameofgod.html