Okay I had a closer look now. Tbh I don't download anything that isn't a major brand product or open-source. I'm guessing the amount of work you put into this you're planning to monetize the app right? If so my first point of feedback would be to support either a web app or mobile app.

I really enjoy the concept behind the app focusing on subjects rather than structured lessons. I enjoy going on learning rabbit holes so this would fit me better than structured lessons.

Lastly a video or demo of the app would help as the UI is quite complex. It's not clear how I would go from importing a web page to using the cards for example.

Feel free to ping me if you have updates - happy to help support another indie dev!