For a large number of Windows and Mac users who have less than 1 TB to backup (or less than 6 TB if they are willing to put up with a fair amount of hassle) there is a far less expensive option.
I speak of Windows and Mac users who got a Microsoft 365 subscription for the Microsoft Office apps. That comes with 1 TB of OneDrive, or 6 TB if you get the family subscription.
OneDrive has API access which is supported by a fair number of commercial and open source backup programs.
You can get a family subscription without being a family. All you actually need is the ability to control 5 extra email addresses, one for each fake family member. Your 6 TB would end up partitioned into 6 1 TB buckets so as I said, would be somewhat of a hassle to use.
But if you only need 1 TB, and want or need Office anyway, and don't really have a lot of non-backup cloud needs, then OneDrive is a good, often overlooked option.