Unfortunately, Windows 11 is not yet available for LTSC versions.
Once Windows 11 is released for LTSC versions, you should be able to upgrade using the same volume license that you have for Windows 10 LTSC. The exact procedure for upgrading will depend on the specific version of Windows 11 and the licensing agreement that you have with Microsoft.
I recommend keeping an eye on Microsoft's official website and announcements for updates on when Windows 11 will be available for LTSC versions and for more information on the upgrade process.
---If the Answer is helpful, please click "Accept Answer" and upvote it.