Ask HN: Strategies for local backups of cloud data?

I use Dropbox and I use Apple's various iCloud storage things (Documents, Desktop, Photos, etc). I believe it's probably true that these companies can do a better job of maintaining my data over the long term, than me, buying HDDs and replacing them before they fail, etc etc etc.

but

What I'm actually afraid of is some screw-up that ends up preventing me from accessing my cloud data. For example a billing screwup. Or a scan-for-prohibited-materials gone wrong. Or a login screwup. Or a straight-up attack from a bad actor. Or simply an infrastructure oops.

Presently I have one machine under my control that I have set so that Dropbox stores all data locally also, and I have tried to do the same with Apple iCloud (though I'm never sure with Apple what is actually happening) ... and then I run a cron job to backup those folders to a NAS onsite.

But I really like the idea of 100% of my data living on the cloud and a far smaller percentage "living" on my local machine at any one time ... especially when the cloud storage total starts getting large w.r.t the size of the HD on my local machine.

Is there some kind of service or program/app that will periodically suck down 100% of my cloud data and stick it on my NAS, without having to actually store 100% on my computer (the one doing the sucking) at any one time?