I think learning guitar would be fantastic!
I have a similar problem, too. I just don't know what my interests are. It's getting a little better now, but when my T asked me a year ago to learn something new, that was a real challenge! I simply wasn't interested in anything!

One way could be to try to remember things from your past. What you liked as a kid or teen. Even if you weren't allowed to do anything by your parents, did you dream of something?
In the beginning, you can just force yourself to try things. You can't know if you enjoy them before you try. If you don't like it, that's fine, try something else. A great motivation for me is watching YouTube videos where people are passionate about their hobbies! Just watching someone being excited makes me want to try it, too. You can watch anything from cooking, baking, reading, art (lots of drawing and painting tutorials!) exercise, pet care,...