概要

using TMPro;
using UnityEngine;
using UnityEngine.Accessibility;

internal sealed class Example : MonoBehaviour
{
    [SerializeField] private TMP_Text m_tmpText;

    private void Awake()
    {
        AccessibilitySettings.fontScaleChanged              += fontScale => Debug.Log( fontScale );
        AccessibilitySettings.boldTextStatusChanged         += isBoldTextEnabled => Debug.Log( isBoldTextEnabled );
        AccessibilitySettings.closedCaptioningStatusChanged += isClosedCaptioningEnabled => Debug.Log( isClosedCaptioningEnabled );
    }

    private void Update()
    {
        m_tmpText.text = $@"fontScale: {AccessibilitySettings.fontScale}
isBoldTextEnabled: {AccessibilitySettings.isBoldTextEnabled}
isClosedCaptioningEnabled: {AccessibilitySettings.isClosedCaptioningEnabled}";
    }
}

Unity 6000.0.10f1 で追加された AccessibilitySettings を使用すると
iOS / Android のテキストサイズを取得できます。

参考サイト様