Duplicate SharePoint Site

How to duplicate a SharePoint Site with a SPFx app inside? There are two ways to do it. One is to use the hidden "Save as Template" feature, another is to use PnP PowerShell.

Use “Save as Template”

1. Follow the first answer here to enable denyaddandcustomizepages using PowerShell.

$adminUPN="[email protected]"
$orgName="antdevstudiosdev002"
$userCredential = Get-Credential -UserName $adminUPN -Message "Type the password."
Connect-SPOService -Url https://$orgName-admin.sharepoint.com -Credential $userCredential

2. Follow this blog post to remove your SharePoint SPFx app temporarily if you have one.
3. Open “Save as Template” page for your site, format like this: https://your-sharepoint-site-url/_layouts/15/savetmpl.aspx.
4. Request access if you have the error “Sorry, you don't have access”, and approve the access using the global admin account from “Access Requests” settings page: https://your-sharepoint-site-url/Access Requests/pendingreq.aspx, or just use the global admin account.
5. The template is available at the solution gallery after generated: https://your-sharepoint-site-url/_catalogs/solutions/Forms/AllItems.aspx.
6. Now with this template you can follow this guide to set up a duplicate subsite or site collection.

Use SharePointPnPPowerShellOnline

Follow scripts in this blog: https://www.sharepointdiary.com/2019/08/copy-site-using-powershell-pnp-provisioning-template.html