Can I use C# 7.3 with .Net Framework 4.6.1?

Question

I'm interested in enum generic constraints, but when I'm switching language version for project on Build → Advanced I'm still getting error «not available in C#5; please use language version 7.3 or greater» even after reopening the project.
Project type is an ASP.NET MVC application.

Answer 1

I've installed Microsoft.Net.Compilers and Microsoft.CodeDom.Providers.DotNetCompilerPlatform packages from Nuget, then changed in web.config system.codedom → compilers → compiler language="c#;cs;csharp" property langversion to 7.3, reloaded project and all worked.