I was a (removed) who recently decided to become Shia Alhamdulilah. I was wondering if it was problematic to believe that the Prophet had other daughters besides Fatima. I had learned as a Sunni that the prophet had other daughters besides Fatima, and I have recently learned that there is no evidence for it. Is believing that the Prophet had other daughters make it so that Fatima has less virtues?

May Allah bless you and makes it easy for you.
Believing that the prophet had other daughters doesn’t reduce the virtues of Sayyida Fatima. Sayyida Fatima is known and Allah and the prophet spoke of her profound virtues. Nothing can change that.
The matter is about fact and accuracy. The fact of the matter as per the historical account is that Prophet had no any other children.
Believing that prophet had other daughters may give values to some of those who stood against the Ahlul bait