Add an existing user to Local Administrators group via Powershell

Add an existing local user to the Administrators group.

Command

# Replace with your local user ID or AzureAD/Entra ID - prefix with 'AzureAD\' for latter case
$User = "username"
Add-LocalGroupMember -Group "Administrators" -Member $User

# Alternative script for AzureAD/Entra
net localgroup administrators AzureAD\<username> /add