Last September, Microsoft officials admitted they were putting the mobile versions of the Microsoft Office applications for Windows on the back burner. Late last week, Microsoft announced the end of support date for those Office Mobile applications: January 12, 2021. After that date, Microsoft won't provide any more security fixes, bug fixes or technical support for those applications.
Microsoft is telling users who already have the apps installed on their Windows Phones before the end of support date will still be able to use the apps. But the apps won't get any security updates, fixes or technical support after January 2021.
Microsoft describes these Office Mobile apps -- specifically Word, Excel, PowerPoint and OneNote -- as "the Office apps for phones using Windows 10 Mobile." Windows 10 Mobile's final end-of-support date is tomorrow, December 10, 2019.
As Microsoft officials said a year ago, company officials decided to prioritize development for the iOS and Android versions of its Office apps and, on Windows, for Win32 and web versions of these apps. As a result, they said they planned to deprioritize the Universal Windows Platform (UWP), touch-first mobile variants.
However, these Office Mobile apps also can work on other Windows devices that are not Windows Phones. Some people use them on Windows tablets, Surface Hub, HoloLens and even the Surface Go because they can be downloaded and used for free. Office Mobile apps are free on devices with screen sizes of 10.1 inches or smaller. I am fairly sure that Microsoft is going to cease supporting these Office Mobile apps for Windows everywhere as of next year. (I asked the company for clarification, but no answer so far.)
Update (December 11): It turns out Microsoft is only going to drop support for these apps for Windows Phones, but will continue to support them on Windows 10 tablets, Surface Hub and HoloLens. I asked whether the word "support" means that Microsoft will continue to provide regular security updates for the Office Mobile apps on these other platforms. I have not gotten a definitive response to that question, but believe the answer is yes, given the boiler plate statement Microsoft is sending to the press:
"This (end-of-support announcement) only applies to the apps on Windows 10 Mobile. We will continue to support them for use on Windows tablets under 10.1. However, the best experience for people who want to use Office on a PC is through the desktop apps with an Office 365 subscription, or the web apps which are available for free to consumers at office.com."
At its Ignite conference last month, Microsoft reversed course with its Win32 version of OneNote. Instead of deprioritizing that OneNote 2016 desktop version, as had been planned previously, Microsoft officials said they'd continue to provide new feature updates for it.