How? The laptop does exist, so at a minimum this is not an outright fabrication, allusions to which I've seen several times in the comments here. The veracity of the photos of crackhead Hunter seems to be also beyond reasonable doubt. As is the fact that he was magically getting millions of dollars for things he has no expertise in, for some reason. The veracity of emails can likely be confirmed by the FBI using DKIM.
A better question would be why this did not come up during the impeachment hearings. There's some exculpatory evidence on that laptop.