Falling through floor when crouching FPS C#,When I crouch my body falls through the floor (FPS)

You cannot directly modify the value of a component in a Vector3, for example the z component in your transform.position transform.position.z. I assume this is because it is read-only. However, the Vector3 itself, isn't and so you can set the value of transform.position.z by modifying transform.position as a whole. For example:

 transform.position = new Vector3
 (
     transform.position.x,
     transform.position.y,
     transform.position.z + 1
 );

@malcah08

Another thing, if you're modifying the position of the player when crouching (don't know why it's the z position and not the y), you might teleport the player into the ground, and so they may slowly descend to their demise. You might want to modify the scale instead, or the camera position, so the player looks like they are smaller or crouching.