“…The mean field game (MFG) [9,34], a very powerful tool in solving problems with large-population characteristic, is applied in many fields such as information technology and engineering [15,28,31], crowd motion [1,8,33], finance and economics [13,19,47,49], vaccination and medicine [5,12,21,24,35], especially for the following recent papers connected to the COVID-19 pandemic [2,14,17]. The mean field optimal control problem, a special class of control problems, is introduce in [6,11].…”