https://wccftech.com/iphone-13-4-core-gpu-slower-performance-than-iphone-13-pro/

The A15 Bionic does not deliver the same graphics performance, and it will all depend on which model you pick. As discussed previously, the more premium iPhone 13 Pro and iPhone 13 Pro Max have a 5-core GPU, while the iPhone 13 and iPhone 13 mini will ship with a 4-core one. Unfortunately, the difference of that single score has a huge difference in performance, as you will soon read about.

In a new Geekbench 5 Metal benchmark run, the A15 Bionic with a 4-core GPU obtained a lackluster score of 10608. The iPhone 12 Pro from last year with its A14 Bionic is not that far behind, with a score of 9123 in the same test. The difference hardly amounts to a 15 percent performance increase between two GPU generations, showing the compromises one less GPU core can make to the entire equation.