ADK 22000 is the latest
but LTSC 2021 MAK Licenses were created after that was released
therefore, it doesn't recognize the keys, it also don't support Office 2021 KMS Host keys
you can grab the updated pkconfig files for LTSC 2021 (from the iso install.wim if not installed yet)
C:\Windows\System32\spp\tokens\pkeyconfig\pkeyconfig.xrm-ms
rename to something like pkconfig_win2021.xrm-ms
place the file here
C:\Program Files (x86)\Windows Kits\10\Assessment and Deployment Kit\VAMT3\pkconfig
edit ProductKeyConfiguration.man with notepad or any xml editor
and add entry for the new file under the line <ProductKeyConfigurationFiles>
<ProductKeyConfigurationFile>
<FileName>pkconfig_win2021.xrm-ms</FileName>
<ApplicationId>55c92734-d682-4d71-983e-d6ec3f16059f</ApplicationId>
<ProductVersion>10.0</ProductVersion>
</ProductKeyConfigurationFile>