VS Code’s Intellisense wasn’t working for me in this lecture’s new Editor script (and stopped working in every .cs in the project, in fact 
) so I found this thread with some things to try to fix the issue https://forum.unity.com/threads/intellisense-not-working-with-visual-studio-fix.836599/
Here are the steps I took though I’m not certain which one/s got it working:
- Close VS Code and in Unity go to Edit > Preferences, then click the “Regenerate project files” button
- Reopen VS Code and open the debugger panel (ctrl + Shift + d) and make a new .json file for the project using the Unity Editor C# plugin (you might already have one set up in your project though)
- In Unity, go to Window > Package Manager and update Visual Studio Code Editor (or the regular VS Editor if you’re using that). For me they were both out of date
- This is perhaps the most important step - restart Unity
After doing these things Intellisense started behaving normally for me again.
Hope it helps!