Is working as a waiter at parties that include prohibited things unlawful, and is the money earned from it unlawful, especially with no alternative except working in construction?

You did well in refusing work that would distance you from Allah. The job of a waiter is permissible in principle, but it becomes forbidden if it involves elements that prohibit it, such as mixing with women, serving forbidden items like alcoholic beverages and pork, attending immoral parties, and listening to musical instruments. This is because it constitutes aiding in sin and transgression, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Your work is impermissible, and its earnings are unlawful due to the presence of these forbidden acts. You must repent and dispose of the money earned by spending it on charitable causes with the intention of getting rid of unlawful gains, not with the intention of seeking closeness to Allah, for Allah is good and accepts only what is good. Whoever abandons something for the sake of Allah, Allah will compensate him with something better. Allah Almighty says: "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect." Praise Allah for having an alternative, which is working in construction.