External hard disks always put to sleep?

Hi,

I have several USB hard disks connected to my Mac mini; most of the time, several of them are mounted at the same time.

I've recently noticed that all of them are put to sleep after idle, despite the fact that “Put hard disks to sleep when possible” in System Preferences is always unchecked (I choose this way). I would understand the other way around, as an app using the disk regularly, but this case puzzles me.

I know disk's firmwares may be configured to put disks to sleep, but I'm sure some of the affected hard disks didn't have this behaviour in the recent past.

I don't know the exact day this behaviour has started. I believe it's either when I bought my Mac mini (shipped with MacOS 11) or when I installed Mac OS 12, some weeks later.

Searching on the Internet led no good results to me.

Has Mac OS X recently changed in this regard?

If not, what else can put idle disks to sleep?