SharePoint Online: Add Top Navigation Link using PowerShell

Requirement: Add link to top navigation in SharePoint Online using PowerShell

How to Add a Link in Top Navigation Bar in SharePoint Online?
To add new link to top navigation in SharePoint Online, follow below steps:

• Login to your SharePoint Online site as an Administrator or a user with Full Control.
• Click on Settings gear >> Site Settings
• Click on "Top link bar" link under "Look and Feel" group
• Now you can add a new link to top navigation bar by entering a Name of the new link, and the URL.
  

If your site template is Publishing site (or site with publishing feature enabled!), you'll get "Navigation" link under site settings. You can add links under "Global Navigation". On communication sites, It gives an easy interface to add links to top menu just by clicking on "Edit" link.

PowerShell to Add Link to Top Navigation in SharePoint Online:
Here is the PowerShell to add link to global navigation of the SharePoint Online site.

#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"

#Add new Link in Top Navigation
Function Add-SPOTopNavigationLink()
{
    Param(
        [String]$SiteURL,
        [parameter(Mandatory=$false)][String]$ParentNodeTitle,
        [String]$Title,
        [String]$URL
    )

    #Setup Credentials to connect
    $Cred= Get-Credential
    $Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)

    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = $Credentials

    #Get the Top Navigation of the web
    $TopNavigationBar = $Ctx.Web.Navigation.TopNavigationBar
    $Ctx.load($TopNavigationBar)
    $Ctx.ExecuteQuery()

    #Populate New node data
    $NavigationNode = New-Object Microsoft.SharePoint.Client.NavigationNodeCreationInformation 
    $NavigationNode.Title = $Title
    $NavigationNode.Url = $URL
    $NavigationNode.AsLastNode = $true

    #Get the Parent Node
    $ParentNode = $TopNavigationBar | Where-Object {$_.Title -eq $ParentNodeTitle}
    
    #Add New node to the navigation
    If($ParentNode -eq $null)
    {
        #Check if the Link with Title exists already
        $Node = $TopNavigationBar | Where-Object {$_.Title -eq $Title}
        If($Node -eq $Null)
        { 
            #Add Link to Root node of the Navigation
            $Ctx.Load($TopNavigationBar.Add($NavigationNode))
            $Ctx.ExecuteQuery()
            Write-Host -f Green "New Link '$Title' Added to the Navigation Root!"
        }
        Else
        {
            Write-Host -f Yellow "Navigation Link '$Title' Already Exists in Root!"
        }
    }
    else
    {
        #Get the Parent Node
        $Ctx.Load($ParentNode)
        $Ctx.Load($ParentNode.Children)
        $Ctx.ExecuteQuery()
 
        #Check if the Link with given title exists
        $Node = $ParentNode.Children | Where-Object {$_.Title -eq $Title}
        If($Node -eq $Null)
        { 
            #Add Link to Parent Node
            $Ctx.Load($ParentNode.Children.Add($NavigationNode))
            $Ctx.ExecuteQuery()
            Write-Host -f Green "New Navigation Link '$Title' Added to the Parent '$ParentNodeTitle'!"
        }
        Else
        {
            Write-Host -f Yellow "Navigation Link '$Title' Already Exists in Parnet Node '$ParentNodeTitle'!"
        }
    }
}
 
#Config Parameters
$SiteURL="https://crescenttech.sharepoint.com/unitedstates"

#Call the function to Add a New Link in Root of the navigation
Add-SPOTopNavigationLink -SiteURL $SiteURL -Title "Support Center" -URL "http://support.crescent.com"

#Call the function to Add a link in "Support Center" node of the navigation
Add-SPOTopNavigationLink -SiteURL $SiteURL -ParentNodeTitle "Support Center" -Title "Application Support" -URL "http://suppport.crescent.com/apps"

Result of the script:

SharePoint Online: PnP PowerShell to Add Link in Global Navigation Menu Bar

#Config Variables
$SiteURL = "https://crescenttech.sharepoint.com"

#Get Credentials to connect
$Cred = Get-Credential

Try {
    #Connect to PNP Online
    Connect-PnPOnline -Url $SiteURL -Credentials $Cred
    
    #Add a Link to Top Navigation Bar
    Add-PnPNavigationNode -Title "Support Center" -Url "http://support.crescent.com" -Location TopNavigationBar

    #Get the Navigation node "Support Center"
    $ParentID = Get-PnPNavigationNode -Location TopNavigationBar | Where {$_.Title -eq "Support Center"}  | Select -ExpandProperty ID
    #Add a link under "Support Center
    Add-PnPNavigationNode -Title "Application Support" -Url "http://support.crescent.com/apps" -Location TopNavigationBar -Parent $ParentID
 
    Write-host "Quick Launch Links Added Successfully!" -f Green
}
catch {
    write-host "Error: $($_.Exception.Message)" -foregroundcolor Red
}