However, in this case, they have ended up giving you 6 months and a courtesy reminder.
If you aren’t interested in maintaining your app annually, don’t publish apps on Apple’s store.
Whether or not their level of notice is enough, they’ve been consistent for years in this practice of 3 months notice for significant and breaking changes, and they seem comfortable compelling annual updates from developers. I would not expect them to care that 3 months is difficult in your circumstances, as they assume you’re prepared to maintain your app and proactively keep up with policy changes over time. It sounds like you did not attend to this year’s policy updates and may well have been out of compliance for months now. Fortunately, they offered a grace period rather than just refusing your next bugfix update. Lucky you!
(I am not sympathetic to your situation, because as a user of apps, I am exhausted of crappy apps and bottom-of-the-barrel behaviors from developers. I understand that others may feel otherwise, and that’s fine too, just as long as those feelings do not get in the way of being a responsive app developer.)