DR Congo qualified for the World Men's Handball Championship for the first time in 2021. Mvumbi was the team's breakout star, playing at midfield. He scored four goals against Argentina and another four goals against 2021 world champion Denmark, despite being double teamed. He totaled 20 goals on 23 finishes and was named the most valuable player in two of DR Congo's matches. His line play during the world championships was described "almost unstoppable". In a wave of notoriety resulting from his performance at the 2021 World Men's Handball Championship, he granted 30 interviews to news outlets around the world. His Instagram account grew from 225 subscribers to 27,000 during two weeks of competition at the national championship.