The UK demands a backdoor in the backups, so having an alternative backup app isn't the solution here. All the alternatives would just get forced into also adding backdoors, or everyone working for the companies that provide alternatives find themselves unable to ever enter the UK again.

That said, I do wish there were more backup solutions for mobile platforms. Android has an API for this, but it's only available to software signed with manufacturer keys. LineageOS and various other custom ROMs use this to allow Seedvault backups, but as a stock Android user I can only pick between Google backups and no backups.

On the other hand, these backups do contain material you don't necessarily want random apps to have access to. Seeing how powerful stalkerware/"parental control" already is on Android, I recognise that there are dangers that the general population might not realise. Adding additional warnings and messages about backups (even when the backups are made using manufacturer software) would probably strike a balance, though.