Mac Office 2019 is now available to purchase as a standalone product, and to download for qualifying Office 365 subscribers. Curiously Microsoft didn’t significantly change the version of the Office apps to reflect the upgrade. Office 2016 apps go up to version 16.16, and Office 2019 apps start out at version 16.17
Microsoft currently supports running Office 2019 on macOS 10.12 Sierra or later. Mac Office 2016 will be maintained until October 2020.