If the Verizon One Talk app is not opening on your device while all other apps function normally, follow these steps to troubleshoot and potentially resolve the issue:

1. Restart Your Device:
- Begin by restarting your Macintosh. Sometimes, a simple restart can resolve app-related issues.

2. Check for Updates:
- Ensure that both your operating system (OS X 10.15.7) and the Verizon One Talk app are updated to their latest versions. Check the App Store for any available updates.

3. Reinstall the App:
- Uninstall the Verizon One Talk app:
- Navigate to the Applications folder.
- Drag the Verizon One Talk app to the Trash.
- After uninstalling, empty the Trash.
- Re-download the app from the App Store and install it again - learn more.

4. Check App Permissions:
- Ensure that the Verizon One Talk app has the necessary permissions to operate:
- Go to System Preferences > Security & Privacy > Privacy tab.
- Verify that the app has access to features like notifications and microphone if needed.

5. Network Connectivity:
- The app may require a stable network connection. Try switching between Wi-Fi and cellular data to see if that allows the app to open:
- Turn off Wi-Fi temporarily and see if the app opens using cellular data.
- If you are using Wi-Fi, make sure the signal strength is strong.

6. Clear Cache and Preferences:
- Sometimes corrupted cache files can prevent the app from starting. Try locating and deleting any preference files related to the One Talk app in your Library folder:
- Open Finder and select Go from the top menu, then hold the Option (⌥) key to reveal the Library option.
- Navigate to the Preferences folder and locate any files that may be associated with the Verizon app. Move them to the Trash.

7. Contact Support:
- If the app still won’t open after trying the steps above, contacting Verizon support directly may be necessary. You can reach them at 800-922-0204 for more specific assistance tailored to your issues with the One Talk app - learn more.

Following these steps should help you troubleshoot the issue with the Verizon One Talk app not opening.