When storing a vehicle for several months to a year, is it better to have the tyres/tires overinflated a little, underinflated a little, or at their regular operating pressure?
Please check YOUR tires for any differing details but Continental says this at:
In cases where the tires will be supporting the vehicle, it is permissible to inflate the tires to the maximum pressure listed on the sidewall. Be sure to return the inflation pressure to recommended usage pressure before operating the vehicle.
This source, at least, does not give any specific recommendation for storage when the car's weight is supported by something else although the original question doesn't suggest that the car is going to be stored other than on its tires. In that case, however, it's safe to assume that the NORMAL operating pressure for the tire is a good choice.