You can use the same principles that Google and friends use to intervene on other behaviors. First you need data to make a model and then you use the model to optimize some metric. In this case it seems like you want to reduce screen time so the intervention in this case would be to lock out applications that seem like unproductive time sinks. Alternatively, you can look into developing better meta-cognitive skills and you don't need extra software for that other than spending some time every day meditating.
You don't even need AI for this. Just track application use and then gradually increase the lockout time for the top 3 applications.
Then a proper question is "what metric to select for optimization?"
As for just using plain software, yes it is an option indeed. But when we are using our devices, we produce so many data points and they are mostly used for hooking our attention through models. Don't you think that there is there so little reverse targeted application of the models?
Getting people to waste time is profitable so that's why AI is used to waste people's time and get them to buy stuff. It's just how the world economy works. If people stop consuming and buying stuff they don't need then the system stops working.
You don't even need AI for this. Just track application use and then gradually increase the lockout time for the top 3 applications.