If only Visual Studio is reporting this, that’s just VS failing in the usual intellisense ways.
If Unity is reporting this in the console, then it’s a real problem, but I just checked and it works fine on Unity2020.1.5f1
This may help you with intellisense problems:
Also, try update the VSCode package inside of Unity: Window → Package Manager → Search for Visual Studio Code Editor → Press the Update button
Also, this: No suggestions in Vscode