The primary loop is battery / engine / air exchanger, with backup resistance heat. Cabin heat pump works off that loop as well.
See the vid I posted. Here’s a screencap with the (low fidelity) diagram.
Primary duty of the heat pump / refrigerant heat exchanger would be heating the cabin, but it also warms up the engine loop and the battery loops as needed just from being at operating temps faster.
In any case, I’ve noted that even in EV modes my cat1 temps are 70/80 degrees (so likely the rest of the engine loop as well).
Remember the system in the Prius/Rav/Yota Hybrid is, in general, calibrated to minimize emissions. It won’t even throttle up/connect the engine until it’s warmed up.