Does this mean that compilation fails without an internet connection? If so, that's horrifying.

Yes, of course it does, isn't it nice?

Even better if you want to automate the whole notarization thing you don't have a "nice" notarize-this-thing command that blocks until its notarized and fails if there's an issue, you send a notarization request... and wait, and then you can write a nice for/sleep/check loop in a shell script to figure out whether the notarization finished and whether it did so successfully. Of course from time to time the error/success message changes so that script will of course break every so often, have to keep things interesting.

Xcode does most of this as part of the project build - when it feels like it that is. But if you want to run this in CI its a ton a additional fun.