[3np]

As the OP notes, MS use their own fork of Mono for the .NET Core runtime these days. So you're not wrong but they are different codebases these days.

[hizanberg]

The .NET Core runtime was never a fork of Mono, it’s always been a separate code base.

[3np]

I never claimed that the .NET Core runtime is a fork of Mono but it certainly contains one: https://github.com/dotnet/runtime/blob/main/src/mono/mono/mi...