I remember having seen that Linux is used a lot by Microsoft's .net team.

Linux is the best platform anyways to run your .net core application. With Avalonia you have a good cross-platform solution, albeit that they still depend on X11/Xwayland for Linux.

A shame .net isn't more popular. The MS branding is a problem though. Although .net core is MIT-licensed, most contributions are from MS¹. Still, if MS would ever ditch it (quite unlikely for the foreseeable future), I think the ecosystem will step up.

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1. F# is an outlier, that is a real community project with lots of contributions from companies and enthusiasts