When you design labels, you would like to use your printer's internal fonts, but you don't see them in the list of fonts in NiceLabel Desktop Designer.
The issue occurs because the Blocking Untrusted Fonts feature is enabled in Group Policy or Registry. You can verify this in the Event Viewer under Application and Service Logs/Microsoft/Windows/Win32k/Operational
You can read more about the Blocking Untrusted Fonts feature on the Microsoft page.