Signal is the world’s most widely used truly private messaging app, and our cryptographic technologies provide extra layers of privacy beyond the Signal app itself. Since launching in 2013, the Signal Protocol—our end-to-end encryption technology—has become the de facto standard for private commu...
Signal provides a backup option. The auto backup for SMS on android is provided by google and likely uses google drive. I don’t know for certain but I would guess the encryption options and security of that route would be impossible to guarantee and the public backlash of signal users knowing their data was being sent to Google’s servers would be massive.
I’ve setup my signal backups to a local folder on my phone. I then have SyncThing running on my phone and home computer so it automatically gets sent once it’s created.