Standing at Arafah on the ninth day of Dhul-Hijjah is the greatest pillar of Hajj — the Prophet ﷺ said, 'Hajj is Arafah.' Pilgrims gather in supplication and remembrance until sunset, and missing it means the Hajj is not valid that year.
References
Jami at-Tirmidhi 889
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.