A controller includes a memory device and an execution device, which executes an operation of an operated unit of an internal combustion engine. The execution device executes a first calculation process that uses adapted data sets in order to calculate an operated amount on the basis of a detected value of a state variable, a second calculation process that calculates, as the operated amount, a value that is determined by a relationship defining data set and the state variable, a reinforcement learning process that updates the relationship defining data set, first and operation processes that operate the operated unit in accordance with a calculated value of the operated amount, and a switching process that switches a process that operates the operated unit between the first operation process and the second operation process in accordance with the state of the vehicle.