I would like to know if there is some extension to VS Code that helps with cleaning code and suggesting more concise code (i.e., hinting for coding best practices).
There are a large number of ways to lint or provide code suggestions or refactoring tips in VSCode, some baked-in or improved with the C# extension.
But if I understand your question right, for something akin to an extension to suggest code simplification, like ReSharper, I would point you to the Roslynator extension. I have used Roslynator2022 (the Visual Studio 2022 version) and like how it links you out to see detailed reasons about the suggestions it makes.
For formatting your code the VSCode Marketplace has multiple good options such as the CSharpier extension.