If you are unable to authenticate in GitHub Desktop, there could be several reasons for this. Here are a few common solutions that might help you to fix the issue:
Make sure that you have an active internet connection and that you are able to access GitHub.com in your web browser.
Check that you have entered the correct credentials for your GitHub account. Double-check that you have entered the correct username or email address and password.
Verify that your account is not locked due to too many failed login attempts. If your account is locked, you will need to wait for the lock to expire or reset your password.
Check if you have two-factor authentication enabled on your GitHub account. If you have, you will need to provide a verification code in addition to your password.
Clear the cache and cookies on your browser. This can fix issues with authentication if your browser has stored old or invalid session information.
Check if there is any issue with the GitHub service, by visiting the GitHub status page.
Check if there is any issue with your network, try to connect to GitHub from a different network or device.
Try re-installing GitHub Desktop, sometimes a corrupted installation could cause authentication issues.
If none of the above solutions work, it’s advisable to check the GitHub Desktop’s official website or the GitHub Desktop’s community for more information and support, or you can contact GitHub support for further help.