Add this script to any UI Element you want to dynamically show or hide (with animation), and set "Open" to true or false show/hide dynamically. Works with ScreenSpace.Overlay and ScreenSpace.Camera UI Canvases

UIPanelToggler.cs

using UnityEngine;

public enum ToggleType
{
    Vertical,
    Horizontal
}

public class UIPanelToggler: MonoBehaviour
{
    public bool Open = false;
    public float ToggleSpeed = 20;
    public ToggleType ToggleType = ToggleType.Horizontal; 
    private Transform _camera;
    private Vector3 _startingScale;
    private Vector3 _offScreenPosition = new Vector3(-10000, -10000, -10000);

    public void Start()
    {
        _camera = GameObject.FindGameObjectWithTag("MainCamera").transform;
        _startingScale = gameObject.transform.localScale;
        if (Open)
        {
            gameObject.transform.position = _camera.transform.position;
        }
        else 
        {
            Vector3 newScale;
            if (ToggleType == ToggleType.Vertical)
            {
                newScale = new Vector3(
                    gameObject.transform.localScale.x,
                    0.01f,
                    gameObject.transform.localScale.z
                );
            } 
            else 
            {
                newScale = new Vector3(
                    0.01f,
                    gameObject.transform.localScale.y,
                    gameObject.transform.localScale.z
                );
            }

            gameObject.transform.localScale = newScale;
            gameObject.transform.position = _offScreenPosition;
        }
    }        

    void Update()
    {
        if (!Open)
            ClosePanel();        
        else if (Open)
            OpenPanel();
    }

    private void OpenPanel()
    {
        gameObject.transform.localPosition = new Vector3(0, 0, 0);
        if (ToggleType == ToggleType.Vertical && gameObject.transform.localScale.y == _startingScale.y) return;
        if (ToggleType == ToggleType.Horizontal && gameObject.transform.localScale.x == _startingScale.x) return;
        var target = ToggleType == ToggleType.Vertical ? _startingScale.y : _startingScale.x;
        gameObject.transform.localScale = GenerateIntermediateScaleVector(target);
    }

    private void ClosePanel()
    {
        if (gameObject.transform.localPosition == _offScreenPosition) 
            return;

        var newScale = GenerateIntermediateScaleVector(0);
        if (newScale.y <= 0.01 || newScale.x < 0.01)
        {
            gameObject.transform.position = _offScreenPosition;
        } 
        else 
        {
            gameObject.transform.localScale = newScale;
        }
    }

    private Vector3 GenerateIntermediateScaleVector(float target)
    {
        Vector3 newScale;
        if (ToggleType == ToggleType.Vertical)
        {
            newScale = new Vector3(
                gameObject.transform.localScale.x,
                Mathf.Lerp(gameObject.transform.localScale.y, target, ToggleSpeed * Time.deltaTime),
                gameObject.transform.localScale.z
            );
        } 
        else 
        {
            newScale = new Vector3(
                Mathf.Lerp(gameObject.transform.localScale.x, target, ToggleSpeed * Time.deltaTime),
                gameObject.transform.localScale.y,
                gameObject.transform.localScale.z
            );
        }


        return newScale;
    }
}


// Example Usage: GetComponent<UIPanelToggler>().Open = true;