It was part of the broader Microsoft Office for Mac update that included Word, PowerPoint, Outlook, and OneNote.
While version 16.61 was largely focused on and bug fixes rather than major new features, it belongs to the version 16 series which introduced:
Access to modern chart types such as Funnel, Sunburst, and Histogram.
Support for co-authoring and AutoSave for files stored on OneDrive or SharePoint.