Prevent dynamic TMP_FontAssets from constantly showing up in your source control

FontAssetSaveDisabler.cs

using System;
using TMPro;
using TMPro.EditorUtilities;
using UnityEditor;
using UnityEngine;

[CustomEditor(typeof(TMP_FontAsset))]
public class FontAssetSaveDisabler : TMP_FontAssetEditor
{
    private static bool FontAssetsLocked
    {
        get => EditorPrefs.GetBool("TMPFontsLocked", false);
        set => EditorPrefs.SetBool("TMPFontsLocked", value);
    }

    public override void OnInspectorGUI()
    {
        if (GUILayout.Button(FontAssetsLocked ? "Unlock Font Assets" : "Lock Font Assets"))
        {
            FontAssetsLocked = !FontAssetsLocked;
            GUIUtility.ExitGUI();
        }

        if (!FontAssetsLocked)
        {
            EditorGUILayout.Space();
            base.OnInspectorGUI();
        }
    }

    // Credit: https://discussions.unity.com/t/tmpro-dynamic-font-asset-constantly-changes-in-source-control/868941/29
    private class SaveHandler : AssetModificationProcessor
    {
        private static string[] OnWillSaveAssets(string[] paths)
        {
            if (FontAssetsLocked)
            {
                int index = 0;
                foreach (string path in paths)
                {
                    if (!typeof(TMP_FontAsset).IsAssignableFrom(AssetDatabase.GetMainAssetTypeAtPath(path)))
                        paths[index++] = path;
                }

                Array.Resize(ref paths, index);
            }

            return paths;
        }
    }
}

How To

Simply create a folder called Editor inside your Project window and add this script inside it. Then, select a font asset and at the top of the Inspector, click Lock Font Assets. While this option is active, the font asset's inspector will be hidden (to avoid accidental unsaved changes) and the font asset won't be saved to the disk. Note that this setting applies to all font assets in the project.