That 90min is the smartctl polling job, but that is not the only thing awaking disks without actual use.
Before 25.10 that could be set to not awake disks in standby with the power mode option: S.M.A.R.T. Service Screen | TrueNAS Documentation Hub
But that option was removed from 25.10.
See HDD Sleep/Spindown/Standby - #71 by ark for a patch that solves the known related issues with 25.10.
I have similar setup with EXOS drives and with the patch they only wake up when I use data from there or during scrubs.