Operator || cannot be applied to opperands type bool and PlayerMovementAdvanced, I'm trying to make the drag only add if these states are the ones the player is in.

private void Update()
{
// ground check
grounded = Physics.Raycast(transform.position, Vector3.down, playerHeight * 0.5f + 0.2f, whatIsGround);

        MyInput();
        SpeedControl();
        StateHandler();
        TextStuff();

        // handle drag
        if (state == MovementState.walking || state == MovementState.sprinting || state = MovementState.crouching)
            rb.drag = groundDrag;
        else
            rb.drag = 0;
    }

if (state == MovementState.walking || state == MovementState.sprinting || state = MovementState.crouching)

Should be

  if (state == MovementState.walking || state == MovementState.sprinting || state == MovementState.crouching)