I heard also that descending at idle can cause shock cooling depending on OAT
AFAIK, that only pertains to piston engines, not turbines.
most jet engines have 'flight idle' where when you pull all the power back at certain conditions of flight, the engine will 'idle' at a higher speed
Not only is flight idle usually a higher RPM than ground idle (usually limited by a minimum fuel flow), but there may be a higher-yet "approach idle" when the anti-ice is on and/or the flaps are down.
The FMS will adjust for approach idle if it is told when icing conditions may be expected.