Signal Secure Backups

Backing up Signal on Android for free and offline was ~always possible. The app creates a multi GB backup file on the phone memory under the Signal folder that you can just copy out and back on a new phone.

The file is encrypted with the passcode and the database can be extracted.

https://github.com/bepaald/signalbackup-tools

If you restore the backup on a new phone, you'll have to resync all desktop machines, and at least on Windows syncing old messages has never worked for me.

Signal never syncs old messages on secondary clients for security reasons.