ok couple things. I also just installed this on Android 10. The app does not appear as an application icon in your app drawer--IT IS A WIDGET AND APPEARS IN THE WIDGETS GROUP! To find it make sure your homescreen is not locked under Settings/Homescreen & Lock Screen Magazine, then under that window, about the 4th item down is "Lock Home Screen Layout"..... make sure that is switched OFF. After that go back to the homescreen and press and hold any place on the homescreen wallpaper and you will go into edit mode where you will see a list on the bottom Widgets, Wallpapers, Effects and Settings. Press Widgets and scroll to the RIGHT until you find it- Then hold the defcon widget with a finger and drag it out of the horizontal list on the bottom of the screen up to a blank place on the home screen wallpaper. Then tap the wallpaper again to go out of edit mode. Then after that go back to Settings. go to Settings/App Management and on the App Management list is App Permissions,. Under that there are 2 things to select at the top of that page-- App Permissions and Apps. Select Apps(the column header on the right) Go down to Defcon Warning System and select it. Turn SMS on. Then select Subordinate Permissions and make sure the SMS/MMS is switched on. This should enable it. If you want to see the latest noticifations and updates touch the widget where ever you parked it on your desktop and it will pop open a window with updates. You should be set.
Hope this helps.