UnityEngine.PhysicsModule is missing?

Hello, brand new unity user here, had an idea for a simple game and wanted to see if I could make it. I've been following a youtube tutorial to get grips on how to make something simple, all I'm trying to do here is make a player move in a simple platformer. I'm using Microsoft Visual Studio for C# scripting and I've been following the tutorial. For the most part I understand everything I've done and the code I have allows the player to move and jump however it allows for infinite double jumps. The tutorial is telling me to fix this issue by adding the lines I have at the bottom using OnCollisionEnter and OnCollisionExit to define whether or not the player is currently colliding with something so that we can script the game to not allow them to jump if they are not colliding.

However, when he types in those commands the program recognizes them, autocompletes them with IntelliSense, they turn blue and everything works out fine. But my program isn't recognizing those commands as something within unity. I searched the unity API and found that both commands are listed under "UnityEngine.PhysicsModule". So I tried adding a line "using UnityEngine.PhysicsModule;" however the program gives me the message "The type or namespace name 'PhysicsModule' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?)"

Maybe I don't know what I'm talking about but it seems that somehow I installed UnityEngine without PhysicsModule, how would I make sure that it is properly installed?