I don't get this. The local-only backup option is already encrypted. Why can't they include an option for me to upload it somewhere of my choosing, like Google Drive, or even using Android's built-in backup system, so I can do it for free (my current backup file is well over a GB)? I already donate $5/mo to Signal Foundation; building a paid-only backup solution gives me a bad taste.
I even wrote a small Android app to do GDrive uploads of the encrypted backup file, watching the local backup directory for new files. (It broke with an Android version update and I haven't gotten around to fixing it.)
The existing local-only option is legacy. I guess they haven't built on top of it because of that. The new option is better, and they say in the article that it should offer an option to do exactly what you ask for.
I even wrote a small Android app to do GDrive uploads of the encrypted backup file, watching the local backup directory for new files. (It broke with an Android version update and I haven't gotten around to fixing it.)