Answer
The answer is "Collective Invention", a 2015 South Korean black comedy film written and directed by Kwon Hyuk-jae. Lee Kwang-soo plays the leading role of Kang Pil-seong, an unemployed man who becomes the legal guardian of a dementia patient to receive government benefits. The film explores Themes of mental illness, social welfare, and the consequences of deception in a comedic yet thought-provoking manner.