I think I might look to others like I lack confidence, because I'm quiet and don't try to boost myself, but it's the opposite: I don't feel the need to make sure people know my strengths because I genuinely don't care what they think of me. Of course, I wouldn't want them to think something terrible about me, but I also wouldn't want them to think I'm special or anything beyond just a regular person.
I'm not sure how I can advise you on this because it comes naturally to me, but perhaps you can think of it as: you are you, and what other people may think is not important when you know yourself and your strengths. If you feel that you don't in fact know your strengths, that is something maybe you can work on. You could try something as simple as making a list of the things that are good about you. They don't have to be accomplishments or skills (though you can include those) but even more basic things about being a human being: you're a good person, you care, you are curious, you are interested in things, there are things you enjoy, and so on. All of the things that make us a human being make us worthy and important (even it not all the examples I gave here apply to you).
All of us are worthy and important.