It’s always been in Jewish tradition that the author of Genesis was Moses, but modern theories have suggested other authors. I believe that the Jewish tradition is correct that Moses is the author of this book. And recently, while reading Genesis, the following verse jumped out at me.
“There they buried Abraham and Sarah his wife; there they buried Isaac and Rebekah his wife; and there I buried Leah” - Genesis 49:31
This is the only place in Genesis where the author leaves his narration and speaks in the first person, placing himself in it. I don’t think it’s just a coincidence that this is right at the end of the book of Genesis and just before Exodus and the story of the life of Moses. Leah is Moses’ great-great grandmother. At first glance, one would probably assume with our modern thinking that this would not be possible. But we have to consider that back then girls got married and started having children soon after puberty, and families were typically large. Plus, Leah probably lived to a very old age and probably lived right there in Egypt with Moses so that he could have gotten to know her as soon as he realized that he was a Hebrew.