There is the option to volunteer in game, maybe they could just add more volunteer related activities and gameplay that sims can do. As it's not a career in the true sense, it could just be a bunch of activities they could do, some rabbit hole, some active tasks, whenever they feel like. Donate plasma, money, supplies, etc. or rise funds by busking, cookie sales, participate in donation drives, etc. Maybe if they do it constantly they could earn some perks like fame points, or they could bring back the good will ambassador trait, or they could get a certificate or award or just a nice picture for some of the activities done. For donating plasma they could get a cookie like they do in real life.