This is always a hard question. Now as a disclaimer I have never actively worked with any of these languages, though I did take a udemy class on C++ so I know a bit more about that.
It seems to me like java and C# are going to be to be the most versatile. C++ CAN be used for anything but it will likely take you a lot longer. It seems to me that C++ is most useful when you need the extreme performance AND have horizontal scaling constraints. For instance a video game has to run on one computer with finite capabilities. For something like a web server or microservice you can just add more servers to handle more load.
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