Hi there! I see you're having trouble downloading the Duolingo app because it says it's incompatible. To help you better, could you tell me where exactly you're trying to download the app from? Is it the Google Play Store or another source? Also, could you confirm the exact message you’re seeing about incompatibility? This will help me figure out why the app isn't installing on your Android 9 device.

In the meantime, here are some things we can check step-by-step:

1. Device Compatibility: Duolingo requires a minimum Android version, usually around Android 5.0 and above, so Android 9 should be compatible. However, some device-specific hardware or software differences might cause incompatibility.

2. Google Play Store Version: Sometimes, an outdated Google Play Store app can cause compatibility messages. Please open the Play Store, tap your profile icon, and go to Settings > About to check for Play Store updates. Update it if available.

3. Clear Google Play Store Cache and Data:
- Go to Settings > Apps > Google Play Store.
- Tap on Storage.
- Clear Cache and then Clear Data.
- Restart your device and try downloading again.

4. Check for System Updates: Go to Settings > System > System updates and make sure your device's software is fully updated.

5. Storage Space: Ensure your device has enough free storage to download and install the app.

6. Try Downloading from Web Version: As a workaround, you can also try installing Duolingo through the Google Play website on your browser by logging into your Google account and selecting your device for installation.

If you’ve already tried these steps, let me know, and we can explore deeper solutions or check for any regional restrictions or server-side issues.

Does this make sense so far? Can you try these and tell me what happens?