Fallback Fonts in Neve
Fallback font families are used while fonts from Google Fonts or Typekit are loading or cannot be loaded at all.
In the Customizer, you can find a global fallback font selector under Typography > General.

This will only contain fonts that are available to the system, even if your computer is offline.
Result
Below you can see how the web page will act inside the browser while loading the fonts. It will first use the fallback font while loading the other ones:
