@pelle @rysiek
For reference, here is the issue about accidentally being discoverable by phone number:
https://github.com/signalapp/Signal-Android/issues/14222

This setting is not reliable and a single failure to set it results in your phone number to ACI (account ID) being revealed. Once revealed, it is difficult to reset ACI, you need to completely unregister and not just reinstall. On Signal server ACI and phone number are stored literally in the same database table of Signal server all the time.

The attack class is not really new though, for Signal "delivery receipts" it is known that they can be used to track when devices get online since at least 2018: https://anarc.at/blog/2018-07-27-signal-metadata/

It is also very similar to "Silent SMS" problem.

So far it looks like this is just a banner to warn that Signal account *may* be deactivated in case of major upgrade, but otherwise everything works.

#Signal apparently requires opening Signal on the phone from time to time without stating the reason. This is version 7.82.0 of Desktop and I don't have Signal on the phone at the moment. "Learn more" leads here: https://support.signal.org/hc/en-us/articles/9021007554074-Open-Signal-on-your-phone-to-keep-your-account-active
I previously thought this only happened during events like PQC migration. Mostly documenting it for myself here.

@david_chisnall In Delta Chat there are no device-to-device delivery receipts ("two empty checkmarks" in Signal: https://support.signal.org/hc/en-us/articles/360007320751-How-do-I-know-if-my-message-was-delivered-or-read) and no automatic error responses. There are read receipts, but they require displaying the message, so cannot be silent and are not sent for reactions. There is a known issue with long-living QR codes/invite links, but this cannot be used to probe online status of someone you just happen to be in the chat with, I posted about it here:
https://support.delta.chat/t/careless-whisper-on-deltachat/4396/2