Dotnet is pretty fast these days. It has a lot more low level control than something like Java, with value types and manual memory management available (it invented the unsafe{} blocks Rust is famous for).

MS even had a prototype version of Windows where the entire OS from the kernel up was managed code (a little excessive, IMO).

Dotnet GUI apps failed on Windows mostly because their UI toolkits are a mess and Electron won the cross platform war. I avoid this stack like the plague, but I write a lot of web backends in C#/ASP.NET (on Linux deploying to k8s) and it's great!