During the FTUE you can enter the schedule step without having any connected calendars

[MelissaAutumn]

Sentry error: https://thunderbird.sentry.io/issues/6072181440/?project=4505428280279040&query=is%3Aunresolved%20issue.priority%3A%5Bhigh%2C%20medium%5D&referrer=issue-stream&statsPeriod=14d&stream_index=1

I haven't tested it but it looks like the user ends up in the setup step after clicking back. For oauth logins during FTUE we set a localstorage token and check that to re-route them to the correct step. It's possible that they've performed a sequence of actions that caused this token to not be destroyed properly during a cancel or something.