Anhedonia: I don't enjoy my hobbies anymore

What you are describing is anhedonia, a core symptom of depression characterized by a reduced ability to experience pleasure. This is a neurobiological state often linked to dysregulation in the brain's reward circuitry, particularly involving dopamine. Behavioral Activation (BA) is a highly effective, evidence-based intervention for this. The counterintuitive principle of BA is "action precedes motivation." Instead of waiting until you "feel like" playing guitar, commit to playing for just 5 minutes at a scheduled time. Often, the action itself slowly helps rebuild the dopamine pathways required for motivation.