How can I disable my player movement and camera movement when I hit I to open my inventory?

I want to stop the player from being able to move, and disable my third person camera from moving when I press I to open my inventory and then re-enable it when I press I again to close my inventory. How can I achieve this?

Use a boolean variable that it’s always checked before the movement operation starts. Then, change it to false when you don’t want a certain something moving, like when you open your inventory.

You do what @MSavioti said, but there’s also a thing for all rigid-bodies Freeze.
To access it, you call the enum Constraint as below:

MyRigidbody.constraints = ...

Now to freeze your object movement, rotation, etc. you just call this way.

MyRigidbody.constraints = RigidbodyConstraints.FreezeAll;
    
//You can also call separated like below...

MyRigidbody.constraints = RigidbodyConstraints.FreezeRotationZ | RigidbodyConstraints.FreezePositionY | RigidbodyConstraints.FreezePositionZ;

To unfreeze the constraints and get back to normal set it to None

MyRigidbody.constraints = RigidbodyConstraints.None;

As per the logic of when to set that, I’ll leave it to you.

Regards.