Not sure on the new model but on the old model the cooler (and heater) is the radiator. The gearbox oil needs to be hot to work properly and keep moisture out. On the new models with the 8-speed box the torque converter is locked nearly all the time now so the oil getting too hot is much less of a problem.
Volvo used to offer an aftermarket gearbox oil cooler kit for the Mk 1 XC90 but only for 2.5T petrol models with the faster revving engine.
So whilst I can't say definitively, I doubt there is one available for the new XC60.
This was the XC90 one :
https://www.volvopartshop.com/oil-co...on-16533-p.asp