Fabric SharePoint Data Connector for Microsoft Graph API using Service Principal Account

We tried to retrieve data from several company SharePoint sites (items/files) using a Service Principal account with Microsoft Graph API granted permissions but the only thing we can get is data "about" sites and not data in sites itself using Office 365 Fabric connector. When we try same thing with Fabric SharePoint Online connector in a Pipeline we get "Invalid Credentials" error. Using Legacy API will work but this means creating a different Service Principal account for every and each SharePoint site. It would be great to have this feature in the future and avoid maintaining a lot of different Service Prinicipal accounts, permissions etc.