What PowerShell can grant a specific user Admin permissions on ALL site collections in SharePoint Online?

@frob ,

SharePoint Online PowerShell to add a site collection administrator for all site collections:

#Variables for processing  
$AdminURL = "https://tenant-admin.sharepoint.com/"  
$AdminName = "******@tenant.onmicrosoft.com"  
    
#User Names Password to connect  
$Password = Read-host -assecurestring "Enter Password for $AdminName"  
$Credential = new-object -typename System.Management.Automation.PSCredential -argumentlist $AdminName, $Password  
   
#Connect to SharePoint Online  
Connect-SPOService -url $AdminURL -credential $Credential  
   
$Sites = Get-SPOSite -Limit ALL  
   
Foreach ($Site in $Sites)  
{  
    Write-host "Adding Site Collection Admin for:"$Site.URL  
    Set-SPOUser -site $Site -LoginName $AdminName -IsSiteCollectionAdmin $True  
}  

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