I turned off "Optimize Mac Storage" on the mac. [1]
I back up all devices to the mac and nothing else [2]
[0] I found 10 being sent to iCloud on the mac, entirely by accident.
[1] Who in their right mind sends their home directory to Apple? I used to put Sun user home directories on NFS for some 300 users, because it was necessary, and I guarded them like crazy.
[2] I turned off iCloud backups when the kids visited. Apparently, they were doing background backups, and my dogshit ISP was returning "Internet Not Available" because uploads destroy the router (on purpose) and they said "Only solution is to get a more expensive plan".
And I back up the computer with the device backups with SuperDuper! (free) to do image/bootable backups, along with TimeMachine (after I move the Downloads directory with all its excess to an external disk)
My trust in computer companies is ZERO. I even keep two email addresses, just in case. And there are insane gotchas. I backed up an iPhone to a mac, and when I went to restore it to a new phone: "Sorry, Dave, You must upgrade your MacOS to do this"
FORTUNATELY, I had separately backed up all iPhone photos to the mac (use ImageCapture) and all files held by apps via "iTunes" file sharing.
Zero Trust model of computing.