In June, Microsoft announced the first preview of Office 2019 for Mac. The upcoming iteration of the suite is intended to be the new option for those still reluctant to make the switch to Office 365, and it includes the same features already available in the subscription variant. Starting next month however, all Office 365 for Mac subscribers will have to upgrade to macOS Sierra or High Sierra in order to receive fresh updates that come with Office 2019 for Mac.
Microsoft quietly announced in an Office support document that Mac users must be running macOS 10.12 or later to update to the latest version of the Office apps for Mac and receive feature releases. This is part of the Office 365 for Mac September 2018 update.
Users will still be able to receive Office support and continue using their version of Office 365 for Mac even if they don't update to macOS Sierra or High Sierra before the update is released next month to all Office 365 subscribers. However, they will not be able to get new Office 365 features.
The full release of Office 2019 for Mac will be available in the second half of 2018. Among other things, it will feature the focus mode in Word and morph transitions, in-click sequence, and 4K video export in PowerPoint. In Excel, there will be new charts and functions.