>> yes but it's no longer a mainstream dev tool really.

C# is currently #5 on Tiobe right behind Java:

https://www.tiobe.com/tiobe-index/

It is just as mainstream as Java and everything else in the top ten.

>> They tried to displace Java but failed.

Enterprises used to be either Linux / Java shops or Windows / C# / VB shops.

Now both Java and C# are being slowly displaced by Containers, Go, and Rust.