How sound is the saying that ‘Umar ibn al-Khaṭṭāb shaved a young man’s beard due to its extreme beauty, and can this be used as an argument for the permissibility of shaving the beard?

It has not been found that Omar (may Allah be pleased with him) shaved a young man’s beard. Rather, it has been narrated that he shaved or trimmed the head hair of a man about whom women were heard to be speaking admiringly. Many scholars have explicitly stated this, among them Shaykh al-Islam in Al-Fatawa al-Kubra and Al-Istiqaamah, Ibn al-Qayyim in Al-Turuq al-Hukmiyyah, and Al-Alusi in his Tafsir. The story is mentioned in detail in Tarikh Dimashq. As for the ruling on shaving the beard, it has been clarified in previous fatwas.