I'm not able to find a way to automatically apply lables to all documents on a SharePoint Online Library.
Is there way to replace classic IRM with Azure Information Protection?
@JoaquinGomez Have you seen this, is that what you are looking for? This feature is in public preview currently:
Use sensitivity labels with Microsoft Teams, Office 365 groups, and SharePoint sites (public preview...
Enable sensitivity labels for Office files in SharePoint and OneDrive (public preview)