Amber don't work properly without Internet access, it even doesn't like my frequent airplane mode toggles.
Discussion
That doesn't sound right
Did you experience otherwise? What's it doing without connection to a relay?
It communicates with other Android apps via intents, it doesn't need a relay unless you use it as a remote signer
Can't test this right now as I'm not using my new Pixel with #GrapheneOS yet (the described problem I experience on another phone, really thought it's Amber not liking my airplane mode usage), but great if it really works that way.