He has topless photographs of his underaged niece, he had to hush his psychiatrist because her parents to her implied he molested her, he has chat messages about her "thinking I raped her" and openly admitted to showing her his naked body. You can go read the leaks right now if you want a source.

Or you can read this highly editorialized version that takes some innocent things out of context, while openly displaying the worst with it (https://bidenlaptopreport.marcopolousa.org/report_viewer/#p=...)