Few have benefited as much from the convergence of a stock market rally and an economy gripped by pandemic as the trading app Robinhood.
Of the roughly six million online trading accounts opened in the first six months of the year, at least three million were at Robinhood. In June, the privately held start-up processed 4.3 million transactions a day, more than any other broker and nearly four times as many as rival E*Trade Financial.
After…