Buttons don't work, clicks on them give no response

[yvolk]

Users of some devices report that "ToDo Agenda" doesn't work for them, and in particular that buttons don't work. Or work only from time to time.

Actually in Android terms this means that "ToDo Agenda" app (sitting behind a widget that is drawn by a Launcher app) cannot / is not allowed to "start activities" e.g. open its own Settings screen or a screen of a Calendar app.

It appears that such problems can be fixed by a User by changing some System setting. More details below.

Android documentation regarding possible restrictions / permissions that may prevent "ToDo Agenda" to respond to clicks normally: https://developer.android.com/guide/components/activities/background-starts
- according to it an app ("ToDo Agenda" in this case) should be allowed to start activities e.g. an activity to add new calendar event, because of this exception:"The app receives a PendingIntent that is sent from a different, visible app."- this "PendingIntent" is sent from a Launcher app.
This explains why in order to run normally "ToDo Agenda" generally doesn't need any special permission (e.g. permission called by different vendors "Start in background", "Run in background", etc.). And this is why most of users don't have such a problem.

At the same time we see that some devices have their own rules to allow applications to run, and to start activities from the background. In these cases a User needs to search for and:

1. Allow for "ToDo Agenda" device/manufacture-specific permissions like "Start in background", "Run in background", "Allow pop-up messages", etc. 
2. Or/and exclude "ToDo Agenda" app from energy saving optimizations...

As an example, this discussion is about fixing widgets when using Nova Launcher: https://forum.xda-developers.com/poco-f1/help/nova-launcher-widgets-clickable-t3841380