Here is the very first sentence from https://dotnet.microsoft.com:

"Free. Cross-platform. Open source. A developer platform for building all your apps."

The download page for .NET which includes downloads for Windows, MacOS and Linux is https://dotnet.microsoft.com/en-us/download

What the GP meant is exactly what they said, "C# and .net 6 are not windows-centric.", sadly it shares a name with .Net Framework which was windows centric.