Is money earned from designing and selling T-shirts with drawings specific to non-Islamic religious or cultural occasions (such as New Year, All Saints' Day, Halloween, and Valentine's Day) in America halal or haram, given that sales are only to non-Muslims?

It is not permissible for a Muslim to make or sell designs related to the religious holidays and symbols of disbelievers, because the Prophet, peace and blessings be upon him, said: "Indeed, Allah Almighty, when He forbids the eating of something, He also forbids its price." And whatever is forbidden to benefit from, it is forbidden to sell and consume its price. The fact that the sale is to non-Muslims does not change the ruling, because disbelievers are addressed by the branches of Islamic law, and it is not permissible to assist in sin. Similarly, the questioner's disbelief in these holidays and his hatred for them does not remove the prohibition.