From the forum:
"In terms of license, you don't need an internet connection. However, Files app loads it's own Javascript, CSS and several plugins from CDN (jsdelivr.com), and this requires internet. We already have a request to allow serving all assets locally (as an option), although in your case that might not be practical as this means Files app is essentially no longer a"single file", but multiple files that you need to be included with each installation (although you could assign a global path perhaps). In any case, for now it's not possible to load Files app without internet."