Controller and control method for internal combustion engine

A controller for an internal combustion engine, wherein

• the internal combustion engine includes a cylinder, a fuel injection valve that supplies hydrogen gas into the cylinder, and a throttle valve that adjusts an intake air amount,
• a first operating condition is set to such a condition of a fuel injection amount of the fuel injection valve and an opening degree of the throttle valve that an air excess ratio in the cylinder becomes greater than or equal to a prescribed value predetermined as a value greater than 1.2 while satisfying a target output of the internal combustion engine,
• a second operating condition is set to such a condition of the fuel injection amount and the opening degree that the air excess ratio in the cylinder becomes 1 or less while satisfying the target output, and
• the controller is configured to execute
• an obtaining process of obtaining the first operating condition and the second operating condition that correspond to the target output, and
• a selecting process of selecting one of the first operating condition and the second operating condition obtained in the obtaining process according to an operating situation of the internal combustion engine.