There is now a notice of the issue in the text the updater presents before updating (German screenshot).
I think it’s safe to assume most of us here would have handled this differently than we witnessed it playing out in practice.
If said Apps really care about security, they should also stop working shortly after security update support runs out for base Android 11 (I guess Fairphone wouldn’t be able to go on much longer with Android 11, backporting patches without Google support), which would be early 2024 if prior Android versions are any indication.
That being said, the time until then could have been put to good use much differently than Fairphone did now.