Well, whatever Agile means in theory, in practice, it almost always leads to situations like the Android Update situation. Of the Google Chrome Update situation, which is only better because everyone is forced to update.

A situation like the Android update situation, though, is completely unacceptable for smoke detectors or other household devices.

No matter how good predictability is, the demand is that these devices are "buy once, just works™". So we need to write stable software for an unstable use case.

But in no case should we end up with serious devices having a support situation like Android, or the SAMSUNG smart devices.

Yes, it will only be written every few decades, but that is fine. It doesn't need to be a huge industry. Just like Washing Machines are mostly made by smaller enterprises.