Is completely abandoning enjoining good and forbidding evil considered a major sin, or is abandoning the denunciation of a single evil considered a major sin?

The obligation of enjoining what is right and forbidding what is wrong is a collective obligation (fard kifaya). However, it may become an individual obligation (fard ayn) for a specific person if no one else is available to undertake it. The prohibition of abandoning it is related to one's ability to carry it out. Leaving the enjoining of what is right and forbidding of what is wrong is a major sin if the wrongdoing (munkar) is major, and a minor sin if it is minor.