No. Due to how large the camera's dimensions are on the iPhone 13, an iPhone 12 can fit in an iPhone 13 case, but an iPhone 13 cannot fit in an iPhone 12 case due to the larger camera module.
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CORRECTION: It ''maybe'' can. Though, that pictured case does not look like an iPhone 12 mini case, it looks more like an iPhone X-style case judging by the size of the camera module.
No. Due to how large the camera's dimensions are on the iPhone 13, an iPhone 12 can fit in an iPhone 13 case, but an iPhone 13 cannot fit in an iPhone 12 case due to the larger camera module.