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No it doesn't. Only works on win10 (phone, PC, tablet & surface hub for the moment, but they are expanding it to hololens and xbox one).

Even Avalon/WPF has been back ported from Vista to WinXP. Afaik, UWP is newer release of WinRuntime (WinRT).

I'll take a look closer to 2023 then, when 8.1 reaches end of life.