It's a tough question. I'm 61, and I've wrestled or pondered it for most of my life. It is not really just one question ("what is my purpose,") but rather a whole series of interconnected questions -- What should I do with my life? What kind of person do I want to be? What really matters? What do I want to spend my limited time and energy doing? What is a good use of my time? Where is meaning to be found? etc. They're all ways of asking the same thing, just from different angles.
I can't tell you what the answer is. I can tell you that it varies not just from person to person, but from time to time, from age to age. My answers to those questions at 61 is a lot different than my answers at 25 or 40.
I would also say that it's not just one thing. People often imagine that they have to come up with the "one right answer" to that question. In my experience, it doesn't work that way, at least not for most. We find meaning/value/purpose in many different things, and we cobble them all together to make a good life. For example, for me, I get meaning/purpose/value in a variety of ways -- caring for animals, devoting myself to learning and personal growth (intellectual, psychological/interpersonal, spiritual), cultivating friendship, enjoying nature, being kind or helpful to others, contributing to causes that matter to me, smacking down narcissists, taking care of myself, laughter, challenging myself to face fears, and doing occasional writing projects. I also have a loose spiritual belief system that helps orient me.
I try to spend time alone, reflecting on these issues. I think that's important. You have to get past the "clutter" of life (mental clutter, busyness, media clutter, social chatter), because you have to go deeper than just the surface. I find writing it out helpful. Writing helps me think things through. I also find reading and watching quality videos helpful.
I don't want to give you the impression that I've got it all figured out. I certainly don't. It's an ongoing process, and I get off track plenty. There have been many times when I've drifted aimlessly or backasswards. Honestly, I don't even think it's possible to have it all figured out, this side of the veil. There are some things we just cannot know. We steer by whatever light we can dimly perceive. It's like a flashlight with a weak battery. You can only see a foot in front of you. So the job is to take that step, and then the next.
I do believe that if you dedicate yourself to learning and being open in this area, the path gets clearer with time. It takes curiosity, introspection, courage, and perseverance.