does it make sense having a regular user account on someone else’s mac with iCloud logged in as a backup/off-site desaster recovery option?
TL;DR -- I don't think you'd get much additional protection beyond what iCloud itself gives you, if it's strictly an off-site portion of your backup plan. I suppose it would help if you needed your offsite backup
and Apple's servers were unavailable. But that's all I can see.
Some thoughts:
Just using iCloud alone can give you a recovery option in some scenarios (e.g., all your local storage media fail, your house burns down, everything is stolen), but doesn't give you protection in other scenarios (e.g., accidental or malicious file deletions, a catastrophic bug in iCloud that deletes files, Apple server errors, "user error", or a need to recover other user accounts or system settings or anything in ~/Library).
(I would never rely
solely on iCloud!!! It's a rather complicated system, and I would always fear that user misunderstanding or a buggy implementation could delete iCloud data suddenly. Still, it's a lot better than having NO backups!)
Now to your question: since iCloud is designed to immediately synchronise on all devices, I don't see how downloading your iCloud files to another person's Mac gives you any
additional protection beyond plain iCloud...
UNLESS that Mac is also backed up at that location with
point-in-time backups (i.e., where you can restore from a previous date/time, not just the most recent backup).
If the offsite Mac only does a single cloning-type backup every day, for example, you've only got one day (at most) to realize that files have been deleted (or maliciously encrypted), before they are also deleted or replaced on the backup drive by the next backup run. That wouldn't be of much value, IMHO. If, on the other hand, the remote Mac is backed up with Time Machine or CCC with significant retention, then those point-in-time backups should allow you to restore those deleted files, up to whatever the retention period is. And
that could have some value over iCloud alone. Of course, IMHO, your own local backup plan should cover that scenario more conveniently.
If you do want to try it, I think your "regular user account" on the remote Mac would need to be logged on at all times in order for the iCloud updates to take place, but I'm not sure about that. In any case, leaving it logged on doesn't really hurt except for a little memory use. The remote Mac's owner can just use Fast User Switching to log into their own account. Note that at every reboot they'd have to log your account in again. (And somehow remember to do that every time!) Doesn't seem as reliable a setup as
I would like.
Does it somehow interfere with the admin account’s find my or other iCloud settings?
No, it doesn't, in my experience. They can still use Find My Mac. My "household" Mac here regularly has two or three users logged in (each with different Apple IDs) for days on end, and I've never seen a problem related to that. Only my account can use Find My Mac.
