How strong was Guan Yu's combat ability in history? Was it a myth in Romance of the Three Kingdoms?

In history, Guan Yu was one of the most important generals of Shu Han during the Three Kingdoms period. In the Battle of Red Cliff, he single-handedly turned the tide and killed the enemy general Cao Ang. In the Battle of Jingzhou, he led the troops to successfully resist the attack of Dongwu, demonstrating outstanding military talent and combat effectiveness. However, the description of Guan Yu in the Romance of the Three Kingdoms was also considered a mythical product by some people. In the novel, Guan Yu was portrayed as a hero whose power shook the world and his combat effectiveness was exaggerated to the extreme. For example, in the Battle of Red Cliff, he single-handedly fought against Cao generals Pang De, Zhang Liao, and others, and finally defeated them. This description was called "mythical Guan Yu" by some history lovers. Although Guan Yu's combat effectiveness had been exaggerated in history, he was indeed a well-respected and outstanding general during the Three Kingdoms period. His military talent and combat effectiveness were well-known throughout history.