Where: https://doc.ibexa.co/en/master/customer_management/cp_page_builder/#assign-portal-to-customer-group

What:

• Add scope/admin to "Next, under the ibexa.system.page_builder configuration key add custom_portal to the SiteAccess list available to Page Builder:..."
• Explain that if you add a container as a location_id, you need to also add mapping. 
• Remove "# custom_portal siteaccess" from portal mapping configuration in config/services.yaml 
• Divide the site in 2 scenarios: one portal with one location_id, multiple portals with container location_id and mapping