Linda Yaccarino is Twitter/X's CEO — but the company's real boss is owner Elon Musk.Alex Wong/Getty ImagesLinda Yaccarino left her job running ad sales for NBC to become the CEO of Twitter about a year ago. How's it going?On the one hand: Not good, at all. Twitter's ad business, which fell in half after Elon Musk bought the company, continues to sputter.