Default label for a document library in SharePoint Online

Configure a default sensitivity label for a SharePoint document library (Microsoft)

When SharePoint is enabled for sensitivity labels, you can configure a default label for document libraries. Then, any new files uploaded to that library, or existing files edited in the library will have that label applied if they don't already have a sensitivity label, or they have a sensitivity label but with lower priority.

Read the full article:

https://docs.microsoft.com/en-us/microsoft-365/compliance/sensitivity-labels-sharepoint-default-label?view=o365-worldwide

More about sensitivity label

Learn about sensitivity labels (Microsoft)

To get their work done, people in your organization collaborate with others both inside and outside the organization.

https://docs.microsoft.com/en-us/microsoft-365/compliance/sensitivity-labels?view=o365-worldwide

Apply a sensitivity label to content automatically (Microsoft)

When you create a sensitivity label, you can automatically assign that label to files and emails when it matches conditions that you specify.

https://docs.microsoft.com/en-us/microsoft-365/compliance/apply-sensitivity-label-automatically?view=o365-worldwide

Use sensitivity labels to configure the default sharing link type for sites and documents in SharePoint and OneDrive (Microsoft)

As an additional configuration to the settings you see in the Microsoft Purview compliance portal for sensitivity labels, you can use these labels to configure settings for the default sharing link type for a SharePoint site or OneDrive account, and for individual documents.

https://docs.microsoft.com/en-us/microsoft-365/compliance/sensitivity-labels-default-sharing-link?view=o365-worldwide