Since you cannot enter with backpacks or bags, is there somewhere to leave them?

If upon entering there is a review of bags and metal detectors

If you know you can't take them, then don't take them or leave them in the car, problem solved

It is best to leave them in the car.

But can you enter with a backpack then? Or do you have to leave it somewhere?

There is a special line for bag and package inspection.