You’re going to have to explain your reasoning to me there. If your fridge is at 4°C and you put something in there at 21°C it will have to transfer an amount

You’re going to have to explain your reasoning to me there. If your fridge is at 4°C and you put something in there at 21°C it will have to transfer an amount of Joules of thermal energy to the internal environment and then the fridge will have to transport that energy out to the kitchen. The amount of energy depends of the specific heat capacity of the item (J/Kg/K). So to drop the temperature of 1kg of stuff from 21°C to 4°C your heat pump needs to work to remove however many Joules the specific heat capacity determines. If on the other hand if your item is at 0°C then it’s going to heat up via heat transfer from the other items in the fridge. This means the internal temperature of the fridge will drop. But this means the heat pump will have to work less to maintain the internal temperature of 4°C. It’s not that the fridge attempts to heat the fridge up. The fridge simply works less because no fridge is perfectly insulated so it’s easy to let the temperature rise.