how are people with favism and G-6-PD protected from malaria?

The mosquito doesn’t have any preference. These people’s blood cells get destroyed faster because the lack of the G6PD enzyme allows the oxygen carried by the RBC’s to damage them (oxygen is toxic without enzymes that protect us). Since their blood cells get destroyed faster, that includes the ones that are infected with malaria, and the infection has less of a chance to get settled. A similar relationship is between sickle cell and malaria.