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 with around 500 stars on GitHub, and it installs from Google Play or F-Droid like any other app. The hard part was the grey itself. Android only lets an app switch the system's colour filter with a permission that no dialog can grant, so out of the box DetoxDroid paints its own grey wash over the screen, and a red badge stays faintly red. Whoever wants the real thing grants the permission once, in about five minutes on the phone itself or with one line from a computer.