Set DefaultToolboxOption to OptionSetting.UseCustomafter setting the CustomDefaultToolbox (to use the CustomDefaultToolbox with newly created projects). Attempting to set the DefaultToolboxOption to UseCustom before CustomDefaultToolbox contains a valid path will be ignored. Conversely, attempting to set the CustomDefaultToolbox back to null or empty string will be ignored if DefaultToolboxOption is currently set to UseCustom. The DefaultToolboxOption must be changed to UseDefault first.
Requirements
Target Platforms: Windows 11, Windows 10, Windows 8.1