Related List not showing in Experience Site

This is working as designed.

• If there are records to show it will display in the related list
• If there are actions the user can take (create a new record, for example) it will display

This is similar to scenario when any given user doesn't have access to the Fields in a related list, the related list won't display empty, but it would be removed from the layout completely.

Users would need to have the "Create" permission added on the their user's profile in order for the related list to "stay" on the page, regardless if the object has a related list record associated to it or not

This is applicable only to Experience Sites using the Salesforce Tabs + Visualforce template. Experience Builder Sites will display the related list regardless of whether the list contains a record or not.