I have been working on my company's intranet sites recently as we have gone through a reorganization and tasked myself with cleaning up navigation between our various SharePoint hub sites. We previously piloted a contextual navigation bar that would show related sites in the hub navigation bar depending on which hub you were in but folks didn't like that all that much so we went with having the same navigation company wide. The downside to this is, as far as I can tell, unless all sites are thrown into a single hub you must update every hub's navigation bar every time you make a change, in my company's case this involves making the same change 9 times. Not great.

I did some quick searches and found that other folks have scripted this out but I didn't really like any of the approaches I saw. This script only needs the PNP PowerShell module and pushes out the hub navigation bar to all hub sites (aside from itself). I am running this on demand when changes are made but this could be easily scheduled to update on an interval or update when something has changed.

Github

<#
    Jake Cross
    9-24-22
    Copy HubSite top nav bar to other hub sites
#>
# Should be home site for tenant
$HomeSite = "https://domain.sharepoint.com"
Import-Module -Name PnP.PowerShell
Connect-PnPOnline -UseWebLogin -Url $HomeSite
# Get a list of hubs that aren't the home site
$hubs = Get-PnPHubSite | Where-Object { $_.SiteUrl -ne $HomeSite }
# Get top level links in menu tree on the home site
$navnodes = Get-PnPNavigationNode -Location TopNavigationBar
Disconnect-PnPOnline
# For every hub that isn't the home site add sharepoint top menu links
foreach ($hub in $hubs) {
    Connect-PnPOnline -UseWebLogin -Url $hub.SiteUrl
    # Remove whatever is currently on the destination hub site hub nav bar
    Get-PnPNavigationNode -Location TopNavigationBar | Remove-PnPNavigationNode -Force
    # For every top level link in menu tree
    foreach ($navnode in $navnodes) {
        Connect-PnPOnline -UseWebLogin -Url $HomeSite
        # Get object of current top level link to be able to grab children from it later
        $navnodeobject = Get-PnPNavigationNode -Id $navnode.id
        Disconnect-PnPOnline
        Connect-PnPOnline -UseWebLogin -Url $hub.SiteUrl
        # Create link on the destination hub site and store it in an object for later
        $topmenuobject = Add-PnPNavigationNode -Location TopNavigationBar -Title $navnode.Title -Url $navnode.url -External
        Disconnect-PnPOnline
        # For every second level link under the current top level link
        foreach ($child in $navnodeobject.children) {
            Connect-PnPOnline -UseWebLogin -Url $HomeSite
            # Get object of current second level link to be able to grab children from it later
            $childobject = Get-PnPNavigationNode -Id $child.id
            Disconnect-PnPOnline
            Connect-PnPOnline -UseWebLogin -Url $hub.SiteUrl
            # Create link on destination hub site and store it in an object for later
            $secondmenuobject = Add-PnPNavigationNode -Location TopNavigationBar -Title $childobject.Title -Url $childobject.url -External -Parent $topmenuobject.id
            # For every third level link under the current second level link
            foreach ($grandchild in $childobject.children) {
                # Create link on the destination hub site
                Add-PnPNavigationNode -Location TopNavigationBar -Title $grandchild.Title -Url $grandchild.url -External -Parent $secondmenuobject.id
            }
        }
    }
}