Microsoft Entra ID Governance 

I had to test an Access Package use case with a least privilege role so I assigned the user Identity Governance administrator role.

To my surprise, this role does not allow adding SharePoint Sites as a resource.

After looking up the Entra ID role, I found out that the SharePoint administrator role is needed to add SharePoint Sites as a resource.

https://learn.microsoft.com/en-us/entra/id-governance/entitlement-management-delegate#required-roles-to-add-resources-to-a-catalog

I added the SharePoint administrator role to the user.

Once I added the SharePoint administrator role, I was able to add the SharePoint sites