Offline Doesn't Work With Desktop C3?

Despite the claims made on this website, when I'm not online, Construct 3 won't even open and if it's open, it is unable to run a preview. Also I can't build my game either as an NWjs game when offline. This is pretty consistent as I've tested it 20 times, 10 while offline, 10 while online.

It should work offline. If it doesn't please file a bug.

How do I do that since you require a project file and I don't even know how to replicate it beyond turning my internet on and off?

Well, in this case a project is not applicable. FYI I just tried it and the desktop build did load just fine after going offline. Make sure you wait for the "ready to use offline" notification before trying.

How do I know if the ready-offline notification appeared already or not? I updated days ago and have been using it since and it still refuses to work when my internet is having connectivity issues that I'm currently trying to iron out.

How do I know if the ready-offline notification appeared already or not?

If it works offline, it already appeared. If it doesn't, it hasn't. If your connection is unreliable and some resources are failing to download, that may prevent it working offline.

So what can I do to fix this?

Get online, run c3, and wait for the ready to use offline notification to show up.

I called my ISP and fixed the connectivity issues and I've opened it 10 times now for 5 minutes a piece or so and it isn't doing it.