Looks like its not using the correct path.
Unity: 2018 LTS
OS: OSX Catalina
TMP: 1.4.1
UnityException: Creating asset at path urce/Fractured_Bolt/Assets/Fonts/mago1.asset failed.
TMPro.EditorUtilities.TMPro_FontAssetCreatorWindow.Save_Bitmap_FontAsset (System.String filePath) (at Library/PackageCache/com.unity.textmeshpro@1.4.1/Scripts/Editor/TMPro_FontAssetCreatorWindow.cs:1274)
TMPro.EditorUtilities.TMPro_FontAssetCreatorWindow.SaveNewFontAsset (UnityEngine.Object sourceObject) (at Library/PackageCache/com.unity.textmeshpro@1.4.1/Scripts/Editor/TMPro_FontAssetCreatorWindow.cs:1210)
TMPro.EditorUtilities.TMPro_FontAssetCreatorWindow.DrawControls () (at Library/PackageCache/com.unity.textmeshpro@1.4.1/Scripts/Editor/TMPro_FontAssetCreatorWindow.cs:1035)
TMPro.EditorUtilities.TMPro_FontAssetCreatorWindow.OnGUI () (at Library/PackageCache/com.unity.textmeshpro@1.4.1/Scripts/Editor/TMPro_FontAssetCreatorWindow.cs:257)
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <df7127ba07dc446d9f5831a0ec7b1d63>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <df7127ba07dc446d9f5831a0ec7b1d63>:0)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at <df7127ba07dc446d9f5831a0ec7b1d63>:0)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:342)
UnityEditor.HostView.Invoke (System.String methodName) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:336)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition, UnityEngine.Rect viewRect) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:310)
UnityEditor.DockArea.DrawView (UnityEngine.Rect viewRect, UnityEngine.Rect dockAreaRect, System.Boolean customBorder, System.Boolean floatingWindow, System.Boolean isBottomTab) (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:361)
UnityEditor.DockArea.OldOnGUI () (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:320)
UnityEngine.Experimental.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:266)
UnityEngine.Experimental.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect)