Microsoft has revealed that Office 2019 applications will only run on Windows 10. On the Windows and Office services support article, Microsoft revealed that you would have to update to Windows 10 if you wanted to use the latest version of Office without purchasing the Office 265 package.
This is clearly a move to push businesses still hesitant to buy Office 365 because Office 2019 releases will not run on Windows 7 professional product key or Windows 8 product key. This has nothing to do with Office on a Mac because it's a separate product, with a completely different release schedule.
Microsoft also changed the support time for Office 2019 with 5 years of main support and "approximately 2 years of additional support."
The Office 2019 Office suite, which will be available in the second half of 2018, includes familiar applications such as Word, Excel, PowerPoint, and Outlook, along with Exchange, SharePoint, and Skype servers for business.
Microsoft plans to release a preview mid-year, primarily for businesses not using Office 365 on the cloud. They also extend Windows 10 product key support to businesses and customers in the education group running certain OS releases. Windows 10, 1511, 1607, 1703, and 1709 are supported in six months to help users migrate to the latest Windows 10.