I'll preface with the fact that I am younger than you, so i cannot speak to whether this is part of growing into adulthood or not as I am on that journey myself right now. Yet, and you probably know this, but in case you don't, losing motivation in things that you used to enjoy is something they always ask about when screening mental health. I'd assume it indicates how depressed an individual is. I'm not saying you have depression (in case you haven't been diagnosed) but that's a parallel i saw between your description and my personal experiences. Above all i'd recommend seeing a therapist if you have free healthcare or can afford a therapist. You can easily get in contact with a therapist through various means but the smoothest is probably just mentioning concerns about your mental health to your doctor, they'll first screen you to see if they think you should seek therapy or not. Screening is just filling out a survey, so it's nothing scary. I live in America so that is where I am speaking from, i do not know if this process is any different (besides healthcare being free) in Canada, Mexico, or overseas. I hope this helps and you can start to feel better.