If you're using Apple Silicon, you need to boot into 1TR (hold down the power button during boot) and enable Reduced Security mode. The Genius Bar probably isn't going to tell you about that sort of thing.
Here is a log of the installer when I attempt:
Device is unsupported: BIPreflightError - Domain: com.apple.BuildInfo.preflight.error Code: 9 UserInfo: {
What I know for sure is that Reduced Security mode turns off the online "phone home" check you described in the OP, but I don't actually know what issue you're encountering.