ZURICH—The Swiss National Bank (SNB) expects to make a profit of around 26 billion Swiss francs ($28.22 billion) for 2021, the central bank said in its provisional results on Friday, as booming stock markets throughout the year added billions to the value of its foreign currency investments. The SNB made a profit of just under 26 billion francs on its foreign currency positions, which include nearly 1 trillion francs worth of stocks and bonds bought during its long campaign to weaken the Swiss franc. The central bank suffered a valuation loss of 100 million francs from its gold holdings, offset by a 1 billion franc profit from its Swiss franc positions, mainly the negative interest rates it charges commercial banks to hold money overnight. As a result, its annual profit is expected to be higher than the 20.9 billion francs profit it made for 2020. The performance means the SNB …