Signal has announced new functionality in its upcoming beta releases, allowing users to transfer messages and media when linking their primary Signal device to a new desktop or iPad. This feature offers the choice to carry over chats and the last 45 days of media, or to start fresh with only new messages.
The transfer process is end-to-end encrypted, ensuring privacy. It involves creating a compressed, encrypted archive of your Signal data, which is then sent to the new device via Signal’s servers. Despite handling the transfer, the servers cannot access the message content due to the encryption.
With the introduction of a cross-platform archive format, Signal is also exploring additional tools for message transfer to new devices or restoration in case of device loss or damage. Users can begin testing this feature soon, with a wider rollout expected in the coming weeks.
XMPP basically uses the same end to end encyption method as Signal, but due to it not being mandatory some things are easier but come with the footgun that you can accidentially disable it (but it is enabled by default in most modern xmpp clients).
Otherwise: since XMPP federates more servers can theoretically see some metadata, but since most servers are small and community run there isn’t a single big target like with Signal where you can siphon off all the metadata. So you can make arguments for both. XMPP: more meta data but decentralized, Signal: less metadata but all in one place.