Office landlords, hit hard by the work-from-home revolution, are resorting to a desperate measure in the real estate world: “handing back the keys.” When this happens, the landlord stops paying the mortgage on the office building or declines to refinance it. The bank or investors who made the loan then repossess the building. Sign up for The Morning newsletter from the New York Times Some of the biggest names in commercial real estate, like Brookfield and Blackstone, have defaulted on mortgages