Hello
Thank you for your question and reaching out. I can understand you are having query related to Add Local User Account to Loc Administrators Group via GPO
Please check under Computer Config - policies - Windows settings - Security Settings - Restricted Groups
You can add whatever accounts you want to the BUILTIN\Administrators group. Just know this GPO will also remove anyone not on the list
You can put also below command and put it into a .bat file and push it through Logon/Startup Script GPO.
net localgroup administrators USERNAME /add
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