As flo said, we are working on a completly new Telegram app that will support audio and actually is ready to playback audio files. You can get a alpha version of it if it's really urgent but, we think it will be ready end of the year.

I think that's the idea of the content hub by design. Every app can only work with his/her own chunks of bits, so if you make a photo send with signal and telegram, then you have 3 copies of that file, because if you delete it on the phone, signal and telegram are still using their copy...

Image {
source: <the link to the Image>
}

is possible in unconfined profile in apparmor apps, but then your app needs a manual approval in the open store

@humungus,
here is an article, why signal uses amazon aws
https://signal.org/blog/looking-back-on-the-front/
The connection to ubports or ubuntu could be the push-notifications-server.
What do you mean by "strange name"? The used namespace is textsecure.nanuc. The textsecure is the historical name of signal and nanuc us the name of the maintainer.

Best