“The word “trinity” isn’t in the Bible.”
So what. However, it is clear from the Bible that God, Jesus, and the Holy Spirit are three in one.
You are making my point for me. There are many inferences made by the books of the Bible that support certain beliefs. Secondly, much of what happened in the life of Jesus was NOT written, please see John 20:30. So, for the Bible to be the ONLY explicit source suggests anything else done by Jesus is of no importance.
However, there has been great debate over the centuries about the divinity of Jesus, the triune God-head, and the Holy Spirit. Ask the Orthodox! Read what Arius taught, etc, etc.
While few Christians today argue either the concept of the Trinity, or the divinity of Christ, it took several hundred years to really iron that out.