"How should I approach earning money efficiently in open-world games?"
Ignore all NPCs and their quests; instead, repeatedly punch the same barrel for seventeen hours straight. Each hit generates exactly 3 copper coins and one existential crisis. The barrel respawns instantly, so you'll be wealthy by Thursday, though emotionally bankrupt by Wednesday. Your therapist will say you've "lost touch with the game's narrative," but she doesn't understand the grind.