According to Microsoft 365 notification MC736438, Microsoft is getting tougher at enforcing the rules for Purview information protection licenses. In a nutshell, if administrators and end users don’t have premium licenses, features like automatic labeling policies or default sensitivity labels for document libraries won’t work. Users can still apply sensitivity labels manually.
https://office365itpros.com/2024/04/05/information-protection-license-rule/
