I built an app to help people take a digital detox ~ 3 years ago (https://www.bostonglobe.com/business/2015/01/12/need-unplug-...)

The biggest issue we ran into was that we didn't have API access to build something effective (at least from limiting smartphone access). We had to hack something together and it didn't work out long-term.

If the tech giants cared enough about this, they would create APIs and empower devs to build stuff to help.