Question Assembly-CSharp could not be found.

I don't know why but I can't find or use Assembly-CSharp like others. How can I change it like others?

 

This may help you with intellisense and possibly other Visual Studio integration problems:

Sometimes the fix is as simple as doing Assets -> Open C# Project from Unity. Other times it requires more.

Other times it requires you also nuke the userprefs and .vsconfig and other crufty low-value high-hassle files that Visual Studio tends to slowly damage over time, then try the above trick.

Barring all that, move on to other ideas:

https://forum.unity.com/threads/intellisense-not-working-with-visual-studio-fix.836599/

Also, try update the VSCode package inside of Unity: Window -> Package Manager -> Search for Visual Studio Code Editor -> Press the Update button

Also, this: https://forum.unity.com/threads/no-suggestions-in-vscode.955197/#post-6227874