Why does my refrigerator leak so much water from this hole at the back?

The water should go through this hole to a evaporator drip at the back over the compressor if it can’t do that then it will flood the bottom of the fridge. Clean the hole with a bit of warm water and a sponge. About the amount of water check the seal for holes or misalignment but generally a lot of condensation water during the summer is because of the moisture in your house combined with multiple door openings.

Adding to this. Typically a fridge with a hole at the back like this, means its a cold plate design without a fan ( most models do not). The cold plate (evaporator plate) may be visible or behind the plastic liner. The intentional design is condensation does ice up on the rear wall. When thermostat cycles off, the condensation tracks down the wall and into drain. Its important for these fridges to not have any food items touching the back wall. That can cause water to divert on to shelves and make it look like a leak on shelves or at the floor of fridge.