What is the purpose of the inner cover? Why is there a hole in it?
The inner cover stops the bees building comb into the roof.
The hole is a feeder hole and should be blocked off unless you are feeding.
The inner cover is there to give the correct “bee space” above the top frames in your hive. It is a kind of “stop building upwards” signal to your bees. The hole is for placing a feeder on top of the cover. If you don’t intend to use a feeder, you may want to cover the hole in case your bees get creative on top of the inner cover and below the roof. Some do, and some don’t, hard to predict so i always cover it - a thin tile will do, or if you want to maintain some ventilation, a piece of #8 hardware cloth.