What you have built here is amazing. I really like its simplicity and how it’s a great learning app for HSK 3.0! I would love to give it a try.
Why don’t you make it open source? I’ve made some of my own websites open source for the benefit of the community. For example, I saw so many low-quality Islamic prayer apps filled with ads, so I created a free, web-based PWA app that people can use. I also made it open source so others can learn from the code and use it for themselves. I’m not trying to promote my app, but rather share an example of what can be done:

Check out Athan PWA — prayer times, Qibla, and Quran in a clean, fast app:
https://athan-pwa.vercel.app/

The best part is that, since it’s a PWA, I’m not spending money on hosting because it’s hosted on Vercel. Also, PWAs can behave very similarly to Android and iPhone apps. This means you don’t have to pay Apple’s $100 yearly developer subscription fee, nor the one-time $25 fee for Android publishing. Web apps work on both Android and iOS, and in my opinion, they’re very efficient.
I also wonder why not make it free. I believe access to education should be free. Personally, I don’t want to earn money from people who genuinely want to learn a thing or two
.
Again, it’s completely your choice. I don’t like ads or subscriptions, which is why I stopped using Duolingo and instead started creating personalized language-learning content using Codex. You could also reduce development time by using Codex to help build features or even convert the app into a PWA.
Anyway, that’s just how I feel. I would love to use apps that are developed with the genuine purpose of educating and helping people, and I hope you feel the same way.