An Android application that automatically activates Ambient display when your phone is charging.
You have to build it and install it.
There's no use in uploading this to the PlayStore, since it requires a permission you can only grant through ADB -- and if you're going to grant it, you might as well read the source code.
It's no beauty (I think I even left some code half-written) and I don't intend to add any more features. If you find it useful, let me know, I may change my mind.
The permission in question:
$ adb shell pm grant io.slezica.ambientcontrol android.permission.WRITE_SECURE_SETTINGS
Works on my machine (tm).