C# runs natively on Linux (have done for many years now). AFAIK even on Azure people prefer to run it on Linux machines (including the place I work for). Performance wise I believe it runs equal to faster. A lot of C# devs (majority) now work on none Windows machines (they were very quick to add support for the new Mac arch as well).
TLDR; C# the language is as good or even better on none-Windows nowadays.