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Introduction:
# German:
Get-LocalGroupMember -Group "Administratoren"
# English
# Get-LocalGroupMember -Group "Administrators"
# Add a local user to the local administrator group
Add-LocalGroupMember -Group "Administratoren" -Member "TOMHOMEDESK\LokalAdmin"
# Check the result:
Get-LocalGroupMember -Group "Administratoren"
Conclusion:
Sources:
https://www.isunshare.com/windows-server/add-a-user-to-local-administrator-group.html