I built an app to solve my own problem. How do I know if it's a real business opportunity? "I will not promote"

So Hye, I'm a young solo founder, and I recently launched an Android app. The idea actually came from my own problem. I used to forget things a lot that were really important to me. So, I started building something that could help me capture these thoughts quickly before I forget. Honestly, in starting, I was just making it for myself only. It's basically an Android app where people can quickly capture their thoughts from notifications or home screen widgets without opening the app. AI processes those thoughts and organizes them into to-do tasks or memories or reminds users based on the type of thought. Basically, i wanted to make something by which I can capture my thoughts in friction of second. But after spending a month and infinite hours in it, I realized that maybe I'm not the only person facing this problem. There might be many people who struggle with the same thing, so I decided to make it publicly available. Now its publicly available but I'm confused about a few things. Is this actually a genuine problem that enough people have, or it's just my own problem? And even if people need it, can I actually build a business around it? Right now, the app is completely free. Users have to put their own AI API key to use it. But I'm not sure if it's the right approach for the long term or how I should think about monetization. So, I wanted to ask here: How can I validate whether enough people genuinely need a product that I made just for myself? How can I figure out the right target audience and position the product? How can I determine whether people would actually be willing to pay for something like this? I'm still learning, and I would really appreciate advice from experienced people here.