Sensitivity labels are automatically applied or recommended for your …

Microsoft 365 can be configured to recommend or automatically apply a sensitivity label to a file or email if it includes sensitive corporate or personal information, such as social security numbers, credit card numbers, or bank account numbers.

https://support.microsoft.com/en-us/office/sensitivity-labels-are-automatically-applied-or-recommended-for-your-files-and-emails-in-office-622e0d9c-f38c-470a-bcdb-9e90b24d71a1