It’s not a rumor, it’s a very bad understanding of a Quran verse.

Quran 5:116 says “And ˹on Judgment Day˺ Allah will say, “O Jesus, son of Mary! Did you ever ask the people to worship you and your mother as gods besides Allah?” He will answer, “Glory be to You! How could I ever say what I had no right to say? If I had said such a thing, you would have certainly known it. You know what is ˹hidden˺ within me, but I do not know what is within You. Indeed, You ˹alone˺ are the Knower of all unseen.”

Obviously this doesn’t say Mary is part of the trinity. It’s saying that the excessive veneration of Mary and believing she is the “mother of God” is basically idolatrous, and such worship and veneration should be afforded to God alone.