You can't see the Windows 11 upgrade in the Remediation center, but LanGuard is still attempting to install Windows 11. You want to ensure that LanGuard does not install Windows 11 on any workstations.
This happens because the Windows 11 upgrade is included in KB3012973 - Feature upgrade to 21H2 or Windows 11.
You can follow the Understanding Dashboard Actions for Vulnerabilities and Patches in LanGuard article to Ignore this patch for the entire network forever or until a certain date. An Ignore example with a different patch is shown in the image below.
After this is done, run a fresh scan on all the machines so they don't show the Windows 11 upgrade as a missing service pack. The update should no longer be available for deployment.