There are no backups available on the iPhone/iPad app, only a device-to-device transfer while setting up a new device assuming your previous device and new device are both iPhones/iPads. This is despite support for apps storing files to the filesystem that was added some years ago now, and many other apps on those platforms supporting backups of custom file formats (or JSON, etc.).

https://support.signal.org/hc/en-us/articles/360007059752-Ba...