Christmas was a convenient adoption of winter festivities that occur around the globe around winter solstice.  If Jesus existed, based on the events the bible claims were going on at the  time of his birth, he would have been born in the summer or fall. But, it's just a book, deal with it.

https://www.ucg.org/the-good-news/biblical-evidence-shows-jesus-christ-wasnt-born-on-dec-25