How to reproduce it:
1. Open the user's attached project "UIToolkit2.zip"
2. In the Project window open a Packages > Local Package folder
3. Right-click on the window and in the context menu select Create > UI Toolkit > Text Settings
4. Observe the Project and Console windows

Expected result: TextSettings asset appears in the Project window
Actual result: TextSettings asset is not created and errors appears in the Console window:
- "Couldn't create asset file! UnityEditor.UIElements.Text.UITKTextSettingsCreationMenu:CreateUITKTextSettingsAsset ()"
- "UnityException: Creating asset at path Packages/UITK Text Settings.asset failed. UnityEditor.UIElements.Text.UITKTextSettingsCreationMenu.CreateUITKTextSettingsAsset () (at Library/PackageCache/com.unity.ui@1.0.0-preview.14/Text/Editor/UITKTextSettingsCreationMenu.cs:36)"

Reproducible with: 1.0.0-preview.14 (2020.3.7f1, 2021.1.6f1), built-in UI Toolkit (2021.1.6f1, 2021.2.0a16)
Could not test with: 2018.4.34f1, 2019.4.25f1 (UI Toolkit is not introduced yet)

Notes:
- Only reproducible when creating a Text Settings file