Visual Studio Code has a habit of changing often, making true diagnosis quite difficult.
Here’s a link with one of the more common issues Syntax highlighting/ Code suggestion not working - Unity Courses / Ask - GameDev.tv
Also, Visual Studio Code has a new plugin that we should be using. Details are here: Syntax highlighting/ Code suggestion not working - Unity Courses / Ask - GameDev.tv
It does concern me, though that there is a problem loading Assembly-CSharp.csproj. Make sure that in Editor/Preferences/External tools, the code Editor is set to VS Code, and then click on Regenerate Project files.