Add group to many SharePoint Online site through PowerShell

You can use the PnP module and the Set-PnPWebPermission cmdlet for that: https://pnp.github.io/powershell/cmdlets/Set-PnPWebPermission.html

1.Create a csv file as following picture show.

2.Run PowerShell codes as the administrator of these site collections.

 $Credentials=Get-Credential  
 $Group = "[email protected]"  
 $PermissionLevel = "Edit"  

 $filePath = "C:\sites.csv"

 $csv = Import-Csv $filePath  
 $sites = $csv.URL  

 ForEach($_ in $sites) {  

      Connect-pnponline $_ -Credential $Credentials  

      Set-PnPWebPermission -User $Group -AddRole $PermissionLevel  -Identity "/"  

 }  

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