RectTransormWidthLock

using UnityEngine;

// Locks width, but not height.
[ExecuteInEditMode, RequireComponent(typeof(RectTransform))]
public class RectTransormWidthLock : MonoBehaviour
{
    private new RectTransform transform;

    [SerializeField] private float width = 1f;

    void Start()
    {
        this.transform = this.GetComponent<RectTransform>();
    }

    void Update()
    {
        this.transform.sizeDelta = new Vector2(width, this.transform.sizeDelta.y);
    }
}