Every individual VP’s role is defined differently. Some have spent most of their time at funerals. Al Gore was given the task of redefining government. Dick Cheney actually ran the government, if some observers are to be believed. Biden was a liaison to Congress and a general adviser to Obama. Mike Pence sucks up to his boss and does his best to clean up messes. What would Kamala Harris do?
(Note to my readers: I refuse to call her an apprentice president, for obvious reasons.)
She would almost certainly be given portfolios relating to race relations and criminal justice. Other than that, she doesn’t have any experience that fills in a gap for Biden. I suspect he will view this as an opportunity for on the job training; the more she learns, and the better advice she gives, the more authority she will receive. At the end, she would be perfectly qualified to step into his shoes.