Hello,
This is a widely reported issue in which a older Windows device continues to appear on your Microsoft account even after it has been removed. The issue may need to be resolved on Microsoft’s server side.
In the meantime, try removing the device again by signing in at https://account.microsoft.com/devices using an InPrivate window in Microsoft Edge or an Incognito window in Google Chrome. You can also try using a different device or network, then follow the same steps to remove the device from your account.
If the issue persists, submit feedback to Microsoft by clicking the feedback icon in the lower-right corner of the Devices page. Describe the issue, provide any relevant details, and then click Submit.