Perhaps it's related to a corporate scandal that emerged in 2021. A company that engaged in unethical practices like fraud or environmental damage. In the story, they could be depicted as the'monster' preying on the public's trust or the environment. The real - life events of how the scandal was uncovered, the legal battles, and the consequences for the company and its stakeholders could form the core of the story.
Another possibility is that it's based on a social justice movement in 2021. There were many around the world. If in a certain place, there was a fight against systemic discrimination. The authorities or the discriminatory system could be the'monster' in the story. The real - life events of protests, negotiations, and the changes (or lack thereof) that occurred could be what the 'Monster 2021 based on true story' is about.
It could be related to a high - profile criminal trial in 2021. For example, if there was a serial killer case where the events were dramatized in the story. The real - life events of the killer's modus operandi, how the police investigated, and the public's reaction could be the basis.