your URL redirected me to https://www.app-learning.com/simplecrypto/en/

Isn't it enough to make the app work on the browser. downloading it to learn and obtain a certificate takes more time. I can have certificate without downloading any app.
Add the course on the Udemy platform, and if the result is good, you can create an application.
If there is backdoors it will be directed at those who have cryptocurrencies and may steal their money.