Why can't some Android phones receive alarm notifications?

To receive alarm notifications, the following conditions must be met at the same time:

1. Enable alarm notifications in the [Alarm-Notification Rules] interface on the CMS PC side;

2. The Android phone needs to have built-in Google services;

3. Enable app notification permissions in the phone system settings;

4. Under private deployment, the app access method must be cloud transfer. (SaaS deployment can be ignored)