The Nokia Lumia 520 running a Windows 10 custom ROM is not a daily driver. It’s a proof of concept. It proves that with enough reverse engineering, even a "dead" platform can run an OS it was never meant to see.
: Custom FFU (Full Flash Update) files allow users to upgrade to versions of Windows 10 Mobile that weren't officially supported, often including permanent "Interop" unlocks for sideloading apps. PostmarketOS : For Linux enthusiasts, the device has limited support for postmarketOS nokia lumia 520 custom rom work