Thank you for your patient!
Recall the changes between spin and no-more-spin is active VIO and VOA services while indoor. Then disable both VIO and VOA service, but motor no longer spin after reboot.
Finally found a solution without flashing the system image:
Step 1: load https://gitlab.com/voxl-public/flight-core-px4/px4-parameters/-/blob/master/helpers/rb5/ekf2_outdoor_gps_mag.params
Step 2: set vehicle param COM_ARM_WO_GPS to 1
Step 3: power cycle RB5
Now arm RB5 after it comes back online, motor spins. -:)
Hope this helps anyone else running into same issue.