Microsoft published an end of support FAQ for Windows 10 Mobile this week. Most of it confirms information that was already available, such as that version 1709, the final major update for the OS, will no longer be supported beginning on December 10, 2019. If your device wasn't eligible for 1709 and you're stuck on 1703 - which only includes the Microsoft Lumia 640 and 640 XL - your end of support date is June 11.
But the firm also said that the creation of new backups for "settings and some applications" will no longer work after March 10, 2020. This is worth noting, although Microsoft also said that photo uploads and restoring from backups will work for up to 12 months after the end of support.
The company also noted that it has no plans to remove historical Windows 10 Mobile updates from servers, and you'll still be able to use the Windows Device Recovery Tool. This is good news for anyone that was afraid that they'll end up resetting their device and find themselves unable to get the latest updates.
End of support means that the device will no longer get updates, but it will still work. Apps can still be downloaded from the Microsoft Store, as long as they target Windows 10 Mobile version 1709 or earlier.