Since IBM i, IBM z, Unisys ClearPath exist, and power the world of insurances and finance, this sentence is obviously false.
> Google didn't write Fuchsia in Go
Indeed, only the TCP/IP stack and volume management tooling, should be easy for you to find out about them.
Then there is this thing called gVisor, it is powering parts of the world that run on top of Google Kubernetes Engine.
Maybe something there for you to learn as well.
> Microsoft uses somewhere approximating 0% .NET/C# code in the Windows core
On the NT kernel, yes, yet good luck using Windows only with the kernel, without the remaining layers, many of which developed in a mix of COM and .NET.
A basic proof how much Windows systems programming experience you have.
Ah then there is this thing called IoT Edge runtime for intelligent devices, written in a mix of Rust and C#.
And before I forget, NVIDIA DRIVE AGX firmware is written in Ada/SPARK.
Bye and learn to grow beyond the Linux bubble.