Hello! I understand you’re having trouble connecting your JBL Tune 520BT headphones with the JBL app and also to Windows 11. Let's work together to get this sorted out.

To start, could you tell me a bit more?
- Are you able to pair the headphones to your Windows 11 PC via Bluetooth at all, or do they not show up as available devices?
- When you mention the app won’t connect, is that the JBL app on your PC or mobile device?
- Have you tried connecting the headphones to another device like a phone or tablet to check if they pair properly there?

This info will help tailor the steps for you.

Meanwhile, here’s a basic step-by-step guide that often resolves these kinds of issues with JBL Tune 520BT and Windows 11:

1. Forget and Re-pair Headphones on Windows 11
- Go to Settings > Bluetooth & devices > Devices.
- Locate your JBL Tune 520BT. Click on it and select Remove device or Forget.
- Turn off Bluetooth, wait 10 seconds, then turn it back on.
- Put your headphones in pairing mode: Press and hold the power button until the LED flashes (usually white/blue).
- On your PC, click Add device > Bluetooth and select your headphones when they appear.

2. Restart Both Devices
- Restart your PC and power cycle your headphones (turn them off, then on again).

3. Update Bluetooth Drivers on Windows 11
- Press Windows key + X, select Device Manager.
- Under Bluetooth, right-click your Bluetooth adapter, select Update driver.
- Choose Search automatically for drivers.
- Restart your PC if an update installs.

4. Run Bluetooth Troubleshooter on Windows 11
- Go to Settings > System > Troubleshoot > Other troubleshooters.
- Find Bluetooth, click Run beside it. Follow the prompts.

5. JBL App Specific Issues
- If using the JBL app, clear its cache (if mobile) or reinstall it.
- Ensure the app has permissions to access Bluetooth on your device.
- Make sure the headphones are not connected to any other device at the same time, which can block app connection.

A few users have found that removing the headphones from the Bluetooth list, turning Bluetooth off and on again, and then re-pairing solves the problem on Windows 111.

Could you try these steps and let me know which ones you have tried or if you notice any change? That way, I can guide you to more advanced options if needed.

Are you satisfied with this approach so far?