Get-SPOHubSiteStructure.ps1

# Get Hub sites
Connect-SPOService -Url "https://[tenant]-admin.sharepoint.com"
$spoHubSites = Get-SPOHubSite

foreach($hub in $spoHubSites){
    $hubSiteId = $hub.SiteId
    Write-Host "$($hub.Title) ($($hub.SiteUrl))" -ForegroundColor Yellow
    $spoSites = Get-SPOSite -Limit All
    foreach ($site in $spoSites) {
        $siteDetailed = Get-SPOSite -Detailed $site.Url
        if($siteDetailed.HubSiteId -eq $hubSiteId){
            write-host " $($site.Title) ($($site.Url))"
        }
    }
}