Microsoft may not be actively developing new features for Windows 10 Mobile anymore, as recently confirmed by an exec, but the company is still supporting some older Windows phones with bug fixes, security updates, and minor improvements here and there. The Windows 10 Fall Creators Update, which started rolling out to PCs yesterday, is one such iterative release for smartphones. However, there are two handsets that will never see this version of the OS making it to them: the Lumia 640 and 640 XL. Microsoft has decided to end software support for the duo with the Fall Creators Update...
Source: https://www.gsmarena.com/microsoft_lumia_640_and_640_xl_wont_receive_the_windows_10_fall_creators_update-news-27799.php