Why doesn't vs code underline errors?

Question

C++ / C#

Tell me if there is any extension or settings for vs code so that errors are underlined in the C # code, for example, variables that were not created, but are used. What I don’t write for some reason, no errors are underlined example:

Answer 1

1. You must have a C# plugin
2. You must have a .net SDK on your computer
3. You must not have a bare file, but a project (there should be csproj next to it)
Here are more details:
https://qna.habr.com /q/947675#answer_1889815
PS: There is .csx for bare files