https://arstechnica.com/gadgets/2019/01/microsoft-windows-10-mobile-support-to-end-so-use-android-or-ios-instead/

Windows 10 Mobile will receive its last patches and security updates on December 10 this year, as Microsoft winds down the last remaining bit of development on its smartphone platform.

The last major notable to the platform was October 2017, when it was bumped to version 1709. At that point, Microsoft ended feature development entirely, shipping only security updates and bug fixes. That's going to come to an end on Patch Tuesday this coming December.