This is overcomplicated to collect money IMHO. All modern OSs can happily backup app files. It is a well-solved problem. If you find this backup method not secure enough (as Signal authors do), fine, encrypt the backup with a special key, exactly as described in TFA, and leave the resulting archive in a location for my chosen phone OS to back it up as it would. All the goals are accomplished, and without charging me money or limiting how many days of media are stored.

Do not get me wrong. Signal is great software and i'd gladly pay for it. Honestly. But not via this underhanded nonsensical way

Hi there, Signal dev here. The Android app does indeed allow you to export encrypted backups to your local device, which you can sync as you wish. That's not going anywhere, and in fact, we have imminent plans to make it better (cross-platform, faster, etc).

If you would gladly pay for it, maybe you could consider donating for Signal.