The implementation feels uncharacteristically crude for Signal. Instead of seamless protections, you just get handed 64 characters you’re told to “store securely.” That’s not realistic: most people will screenshot it, and those screenshots will end up in unencrypted cloud backups.

Sure but the key is still in a separate location from the backup. Signal can't decrypt the backup and if Signal is hacked someone would still need to get your screenshot to decrypt the backup. Not perfect but far better than an unencrypted backup.