SharePoint Online: Grant Permission to Each Folder in a Document Library using PowerShell

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"

#Set Config Variables
$SiteURL = "https://crescent.sharepoint.com/sites/marketing"
$ListName = "Documents"
$UserAccount = "[email protected]"
$PermissionLevel= "Contribute"

#Function To call a non-generic Load Method
Function Invoke-LoadMethod() {
    Param(
            [Microsoft.SharePoint.Client.ClientObject]$Object = $(throw "Please provide a Client Object"), [string]$PropertyName
         )
   $Ctx = $Object.Context
   $Load = [Microsoft.SharePoint.Client.ClientContext].GetMethod("Load") 
   $Type = $Object.GetType()
   $ClientLoad = $Load.MakeGenericMethod($Type)
    
   $Parameter = [System.Linq.Expressions.Expression]::Parameter(($Type), $Type.Name)
   $Expression = [System.Linq.Expressions.Expression]::Lambda([System.Linq.Expressions.Expression]::Convert([System.Linq.Expressions.Expression]::PropertyOrField($Parameter,$PropertyName),[System.Object] ), $($Parameter))
   $ExpressionArray = [System.Array]::CreateInstance($Expression.GetType(), 1)
   $ExpressionArray.SetValue($Expression, 0)
   $ClientLoad.Invoke($Ctx,@($Object,$ExpressionArray))
}

#Function to Add User to Folder Permissions
Function Grant-SPOFolderPermission() {
    Param(
        [Microsoft.SharePoint.Client.Folder]$Folder, 
        [String]$UserAccount, 
        [String]$PermissionLevel
        )
    Try {

        #Check if Folder has unique permission already
        Invoke-LoadMethod -Object $Folder.ListItemAllFields -PropertyName "HasUniqueRoleAssignments"
        $Ctx.ExecuteQuery()

        If($Folder.ListItemAllFields.HasUniqueRoleAssignments -ne $true)
        {
            #Break Folder Permission inheritence - Keep all existing folder permissions & Item level permissions
            $Folder.ListItemAllFields.BreakRoleInheritance($True,$True)
            $Ctx.ExecuteQuery()
            Write-host -f Yellow "`tFolder's Permission inheritance broken..."
        }

        #Get the SharePoint User
        $User = $Ctx.Web.EnsureUser($UserAccount)
        $Ctx.load($User)
        $Ctx.ExecuteQuery()

        #Get the role required
        $Role = $Ctx.web.RoleDefinitions.GetByName($PermissionLevel)
        $RoleDB = New-Object Microsoft.SharePoint.Client.RoleDefinitionBindingCollection($Ctx)
        $RoleDB.Add($Role)
          
        #Assign permissions
        $UserPermissions = $Folder.ListItemAllFields.RoleAssignments.Add($User,$RoleDB)
        $Folder.Update()
        Write-host -f Green "`tAdded User to Folder Permissions!"
    }
    catch {
        write-host "Error in Grant Permissions: $($_.Exception.Message)" -foregroundcolor Red
    }
}

#Get Credentials to connect
$Cred = Get-Credential
  
Try {
    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.UserName,$Cred.Password)
 
    #Get the List
    $List = $Ctx.web.Lists.GetByTitle($ListName) 
    
    #Get Sub-Folders of the List
    $SubFolders = $List.RootFolder.Folders
    $Ctx.Load($SubFolders)
    $Ctx.ExecuteQuery()
     
    #Iterate through Each Sub-Folder
    ForEach($Folder in $SubFolders)
    {
        #Exclude "Forms" and Hidden folders
        If(($Folder.Name -ne "Forms") -and (-Not($Folder.Name.StartsWith("_"))))
        {
            #Get the Folder's Server Relative URL
            Write-host -f Yellow "Granting Permissions on Folder:"$Folder.Name
            Grant-SPOFolderPermission -Folder $Folder -UserAccount $UserAccount -PermissionLevel $PermissionLevel
        }
    }
}
catch {
    write-host "Error: $($_.Exception.Message)" -foregroundcolor Red
}

#Set Variables
$SiteURL = "https://crescent.sharepoint.com/sites/Marketing"
$ListName="Documents"
$ParentFolderURL = "/Shared Documents" #Site Relative Path of the document Library
$UserAccount = "[email protected]"
 
#Connect to PNP Online
Connect-PnPOnline -Url $SiteURL -Credentials (Get-Credential)

#Get all Folders from the given location - Exclude Hidden
$AllFolders= Get-PnPFolderItem -ItemType Folder -FolderSiteRelativeUrl $ParentFolderURL | Where {($_.Name -ne "Forms") -and (-Not($_.Name.StartsWith("_")))}

#Iterate through each Folder
ForEach($Folder in $AllFolders)
{
    Write-host ("Granted Permission to '{0}' at {1} " -f $Folder.Name,$Folder.ServerRelativeUrl)
    #Grant Contribute permissions to the Folder
    Set-PnPListItemPermission -List $ListName -Identity $Folder.ListItemAllFields -User $UserAccount -AddRole 'Contribute'
}