MEXICO CITY—Passenger traffic at Grupo Aeromexico in December reached its highest level since the start of the COVID-19 pandemic, the Mexican airline said on Thursday. Aeromexico transported 1.74 million passengers last month, or 98.9 percent of the 1.76 million people it moved in December 2019, the company said in a statement. Aeromexico’s total offer, measured in available seat-kilometers (ASKs), was equivalent to 82.6 percent of the capacity of December 2019, the company said. Domestic capacity was up 13.6 percent from December 2019, while international capacity was 70.7 percent of that month. Aeromexico filed for Chapter 11 bankruptcy protection in the United States in 2020 as demand cratered amid the pandemic. In December it unveiled details of a tender offer valuing its outstanding shares near zero as part of its reorganization plan, sparking a sell-off in the stock. The positive traffic figures did nothing to help the airline’s long-suffering stock price, …