Hi Kathy,
Is this a Surface device? If so, the thin black lines appearing only on the taskbar might be caused by a graphics driver glitch or a rendering issue in Windows 11.
Have you tried any troubleshooting steps yet? I’d suggest updating your graphics driver through Windows Update or Device Manager.
Or connecting an external monitor to see if the lines appear there too. If they don’t, it could point to a hardware issue with the built-in display.
Since your device is still under warranty, it’s a good idea to check this soon. If the issue turns out to be hardware-related, Microsoft should be able to help with a repair or replacement. https://support.microsoft.com/en-us/topic/check-your-microsoft-warranty-and-create-service-orders-644472b2-df94-41c7-a67d-2ac6577fc5f3