So I’ve just had this problem with the small 12V battery running completely flat, so much so, the car could also not be taken out of Park gear to push it out of the garage, nor would the boot lid open. The traction battery was still 7/8 full but the car needs the 12V battery to power the electronic first. That 12V battery is a tiny 35Ah battery so does not last long without usage, especially with my ODB2 diagnostic plug left plugged in.
So yes its recommended you either drive it or run it in Ready mode once a week. There are also videos explaining how to do an emergency jump start from under the front bonnet but that’s no good if you can’t push your car out of the garage (if this happens you’ll need to left the seat as the 12V battery is usually sitting there.
Seems plenty of hybrid owners are experiencing these problems during lockdowns – see Will my Toyota hybrid be okay if I don’t drive it for a long time? – Toyota UK
We’re encouraged to ‘park it’ and leave our cars at home if we can, but does a Toyota hybrid need special car maintenance if we don’t plan to drive it?