DetoxDroid

Most digital detox apps are opt-in: start a timer, put the phone down and then hope you stick to it. DetoxDroid turns that around: the quiet phone becomes the normal state, and you take deliberate breaks out of it.

In practice that means the screen stays mostly grayscale, with exceptions for the apps where colour actually carries information (the camera, for one). Do Not Disturb is on unless you say otherwise. Chosen apps are disabled during detox hours, and anyone scrolling too long and too hard gets an interruption to pull them out of the doomscrolling trance. A commitment password locks the settings, so the version of you at 1am cannot overturn what the sensible one decided.

It is free software, around 500 stars on GitHub. Some of its features need privileged permissions that Google Play will not grant, so it is best installed with an ADB script rather than from the store. That makes it a bit technical: it costs a few users, and in return the feature list is an honest one.