SPO - Add Document Library to Quick Launch using Powershell

As part of an SPO site creation script, I'm trying to get newly created document libraries automatically added to the Quick Launch navigation links.

I'm running this code:

$SPOCredentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($userName,$password)

$Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($siteUrl)
$Ctx.Credentials = $SPOCredentials

$web = $Ctx.Web
    $navColl = $web.Navigation.QuickLaunch
    $newNavNode = New-Object 
Microsoft.SharePoint.Client.NavigationNodeCreationInformation
    $newNavNode.Title = "External Documents"
    $newNavNode.Url = "External Documents/Forms/AllItems.aspx"
    $newNavNode.AsLastNode = $false

$navColl.Add($newNavNode)

    $web.Update()
    $Ctx.Load($navColl)        
    $Ctx.ExecuteQuery()

But it's returning this:

format-default : The collection has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested.
+ CategoryInfo          : NotSpecified: (:) [format-default], CollectionNotInitializedException
+ FullyQualifiedErrorId : Microsoft.SharePoint.Client.CollectionNotInitializedException,Microsoft.PowerShell.Commands.FormatDefaultCommand

Any ideas please?

Thanks