I had a similar idea. About two years ago my kid was playing a simple mobile game with her friends a lot. There are many variations of the game theme but they are all ad infested privacy nightmares listlessly fiddled together.
I thought we could do better and make a good and ethical version - also as an educational project. The game turned out well, but we haven't published it yet. It is still planned, but I had to learn free apps apparently are an uphill battle in walled garden ecosystems.
If you think about it, it makes sense: Apple and Google don't like to get their 30% cut from nothing. I believe that is the deeper reason apps like ours are so rare.