QuietEngineer That's likely a response by Tier 1 support who are going through their standard troubleshooting steps before forwarding the ticket to Tier 2/3. Even though these are not relevant here, Tier 1 likely doesn't understand that and are just doing what their supervisors require of them. It's beneficial to reply to each of their questions to avoid more back and forth with them.
The Unplugged phone is of course completely irrelevant here. Their response "Third party distributions are not supported." is a line they didn't use when replying to me. Although GrapheneOS is not supported – as in they are not going to offer GrapheneOS users assistance with troubleshooting issues – that's not relevant to the fact that they are blocking alternate OSs completely, including a secure OS. According to the Play Store entry, they are allowing devices with Android 5 – which stopped receiving security updates 8 years ago – to use the Authy app. Security-wise, that of course doesn't make sense.