Being poor is a full time job. I have fasted for weeks without problems and yet on the one occasion in the last 20 years where I was unable to buy food for three days the hunger was severe and overwhelming - the experiences had nothing in common. The cognitive load I have seen on friends struggling with poverty is immense - they are permanently mentally exhausted of all the hard decisions and complicated math needed…
It's a good idea, but saving money often has an up front cost and I think an app to help the poor would fall into that category.
The people that would end up benefiting from such an app would be people that could afford to purchase a device to run the app.