OK, so to start, I need to make a categorical statement about the doctrine of the Trinity, which may come as a surprise to some people: the doctrine is not explicitly taught anywhere in the Bible, and in fact is never even mentioned in the Bible. That doesn’t mean it’s not theologically true, or even metaphysically true. And it doesn’t mean that the Bible proved irrelevant to developing the doctrine over time. It still could be true: the Bible doesn’t teach *most* of the things that are true!). Moreover, it still could be based on the Bible: lots of things that Christians insist are true can be based on the Bible even if they are not explicitly stated there. Some Christians insist the Bible opposes abortion; others insist the Bible supports a woman’s right to choose; some Christians claim that the Bible teaches that the Kingdom of God arrived on earth on the Day of Pentecost, other Christians say the Bible teaches it will arrive in 2021, others say it ain’t comin’ at all; some Christians insist that the Bible teaches that God will send the majority of people who have ever lived to eternal torment in hell, other Christians claim that the Bible teaches that in the end all will be saved.
https://ehrmanblog.org/is-the-trinity-in-the-bible/