Is a mother entitled to prevent her daughter from marrying someone due to a difference in nationality, and what should the young man do regarding the mother’s rejection?

Starving oneself and refraining from food until death is a form of suicide and intentional self-killing, which is forbidden in Islam, as Allah Almighty says: (And do not kill yourselves. Indeed, Allah is ever Merciful to you), and its punishment is Hellfire, as mentioned by the Prophet, peace and blessings be upon him. Therefore, a Muslim must be patient and hold fast to Allah.