Hello Phyo Zaw Kyaw,
Thank you for posting in Microsoft Community forum.
There's currently no way to directly upgrade Windows 10 Enterprise LTSC to Windows 11 Enterprise LTSC because Windows 11 Enterprise LTSC hasn't been released yet. If Windows 11 Enterprise LTSC is released in the future, you may need to do a clean install instead of a direct upgrade, and you'll need to see if your license agreement covers the new version.
I hope the information above is helpful.
If you have any question or concern, please feel free to let us know.
Best Regards,
Haijian Shan