How to set and force C# language version?

[ghost]

For example, Mono is stuck at C# 8. I can't send C# 11 code to people who use Mono and expect it to compile for them. Yes, there are various Polyfills projects on Github to allow the use of new language features on older runtime, and they support Mono too. But I can't assume the Mono users know how to use or want to use these Polyfills.

[MichalStrehovsky]

Does--langversion do what you need?