There are a few different components involved in the answer.
As pointed out above, the C# 8 compiler is bundled with the .NET Core 3.1 SDK. It's support cycle ends with .NET Core 3.x.
But, the question of C# 8 language support is different: The C# compiler can be configured to conform to any previous language version. See this page for details on how to make that configuration option.
More importantly, the newer versions of the language (and all newer versions of the compiler) do support all the C# 8 language syntax. You can look here and here to see the small list of breaking changes in the language syntax in all versions. They mostly affect edge cases.
Functionally, C# source code, written to match any version, is supported by any compiler beginning with that version.
I hope that meets yours needs. If not, can you add why you are targeting C# 8, and I can help detail the components needed that are supported.
C# / .NET Content