All working but codex.

Assets/Scripts/UI/Menus/Components/ScrollableTextBox.cs

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+using TMPro;
+using UnityEngine;
+using UnityEngine.UI;
+
+namespace BriarQueen.UI.Components
+{
+    [ExecuteAlways]
+    public class ScrollableTextBox : MonoBehaviour
+    {
+        [SerializeField] private TextMeshProUGUI                       _text;
+        [SerializeField] private RectTransform                         _content;
+        [SerializeField] private BriarQueen.UI.Menus.VerticalScrollbar _scrollbar;
+
+        private RectTransform _textRect;
+        private LayoutElement _layoutElement;
+
+        private void Awake()
+        {
+            Init();
+        }
+
+        private void OnValidate()
+        {
+#if UNITY_EDITOR
+            UnityEditor.EditorApplication.delayCall += () =>
+            {
+                if (this == null) return;
+                Init();
+                if (_text != null && !string.IsNullOrEmpty(_text.text))
+                    ApplyTextHeight();
+            };
+#endif
+        }
+
+        private void Init()
+        {
+            if (_text != null)
+            {
+                _textRect      = _text.GetComponent<RectTransform>();
+                _layoutElement = _text.GetComponent<LayoutElement>();
+                
+                if (_layoutElement == null)
+                    _layoutElement = _text.gameObject.AddComponent<LayoutElement>();
+            }
+        }
+
+        private void ApplyTextHeight()
+        {
+            _text.ForceMeshUpdate();
+            var height = _text.preferredHeight;
+
+            if (_layoutElement != null)
+                _layoutElement.preferredHeight = height;
+
+            if (_textRect != null)
+            {
+                var delta = _textRect.sizeDelta;
+                delta.y = height;
+                _textRect.sizeDelta = delta;
+            }
+
+            if (_content != null)
+            {
+                Canvas.ForceUpdateCanvases();
+                LayoutRebuilder.ForceRebuildLayoutImmediate(_content);
+            }
+        }
+
+        public void SetText(string content)
+        {
+            if (_text == null) return;
+
+            _text.text = content;
+            _text.ForceMeshUpdate();
+
+            var height = _text.preferredHeight;
+
+            if (_layoutElement != null)
+                _layoutElement.preferredHeight = height;
+
+            if (_textRect != null)
+            {
+                var delta = _textRect.sizeDelta;
+                delta.y = height;
+                _textRect.sizeDelta = delta;
+            }
+
+            // Also resize Content to match so scrollbar measures correctly
+            if (_content != null)
+            {
+                var delta = _content.sizeDelta;
+                delta.y = height;
+                _content.sizeDelta = delta;
+
+                var pos = _content.anchoredPosition;
+                pos.y   = 0f;
+                _content.anchoredPosition = pos;
+            }
+
+            if (Application.isPlaying)
+                StartCoroutine(RebuildNextFrame());
+            else
+                _scrollbar?.Rebuild();
+        }
+
+        private System.Collections.IEnumerator RebuildNextFrame()
+        {
+            yield return null;
+            Canvas.ForceUpdateCanvases();
+            LayoutRebuilder.ForceRebuildLayoutImmediate(_content);
+            yield return null;
+            _scrollbar?.Rebuild();
+            _scrollbar?.SetNormalized(1f);
+        }
+
+        public void Clear()
+        {
+            if (_text == null) return;
+            _text.text = string.Empty;
+
+            if (_layoutElement != null)
+                _layoutElement.preferredHeight = 0f;
+
+            if (_textRect != null)
+            {
+                var sd = _textRect.sizeDelta;
+                sd.y   = 0f;
+                _textRect.sizeDelta = sd;
+            }
+
+            if (_content != null)
+            {
+                var pos = _content.anchoredPosition;
+                pos.y   = 0f;
+                _content.anchoredPosition = pos;
+            }
+
+            _scrollbar?.Rebuild();
+        }
+
+        public void ScrollToTop()    => _scrollbar?.SetNormalized(1f);
+        public void ScrollToBottom() => _scrollbar?.SetNormalized(0f);
+    }
+}