I'd suggest that lack of support also means that people at Microsoft won't be testing services against Windows 10 Mobile any more, but we all know that they haven't been doing this for some time, sadly. Theoretically, the OS is now 'vulnerable', though in practice Windows 10 Mobile is now battle hardened and also an utterly miniscule target for attackers, so the lack of updates won't actually be an issue. The last update was in January 2020 - and was for the newest 1709 branch. Note that some dates are approximate, since we can't see into the future with certainty! I've colour coded table cells, with pale red for 'on the way out, with workarounds and caveats', through increasingly dark shades, and red for 'no hope!'.

Which means that it's hard to keep track of it all - hence the table below, which I'll keep updated every month. Post the final OS update by a full two years we're in a declining phase of the OS, where most of the stuff that ever worked properly still works, but things are definitely now falling off the edges, as it were.

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