What is the ruling on working in the field of makeup, specifically from home, in Germany, with both veiled and unveiled clients, and is there any sin incurred by a woman practicing this profession, given the possibility of clients displaying their adornments in mixed gatherings?

Working with makeup is permissible, but it is not allowed to apply it to someone whom it is known or highly probable will display it ostentatiously before non-mahram (definition) men. This is because it constitutes aiding in sin, as Allah Almighty says: "And do not cooperate in sin and aggression." It is safer to avoid this work for those residing in non-Muslim countries, due to the difficulty of limiting the work to only those who will not display the makeup ostentatiously.