How is one to deal with lack of enthusiasm? When the point is not that "I do not know what I want", but that "I do not want anything, I do not find joy in activities, dreams, projects".
Lack of enthusiasm and interest in life, indicates that something is amiss. There is joy, love, beauty, power and knowledge in every moment of life experience. Young children naturally live life with interest and enthusiasm. When boredom, joylessness and jadedness begin to overtake life it usually means that it is masking a history of disappointment, rejection and fear. The mask of disinterest is there to protect one from risking further disappointment and pain. The idea is that if you to want anything and don’t try for anything, then you can’t fail or be hurt. Of course it doesn’t work that way in practice. In actually, such people only burying their pain, not healing it, so they are living a life of inner pain while feigning disinterest. My advice is to ask yourself what you are afraid of. Then ask what would be fun and interesting for you to do if you weren’t afraid of anything bad happening. From that you will discover what your joy in life is as well as what fears you need to release.