A change in how Office apps apply mandatory labeling as dictated by sensitivity label policies means that both new and old documents are processed. New documents have always been dealt with; the change being made ensures that Office apps detect the lack of a label when opening an existing document and will apply mandatory labeling at that point. It’s a change to help customers move on from the unified labeling client.
https://office365itpros.com/2021/12/17/sensitivity-labels-policy-information-protection/
