According to the most famous Japanese website, Apple is going to launch four iPhones in 2021. The iPhone 13 will have similar design to iPhone 12 with several slight changes.
According to the report, the height and the width of the four iPhones are expected to remain the same. At the same time, the thickness will probably increase by about 0.26 mm. The report also added that the size of the rear camera unit of all iPhone 13 models will increase by 0.9 mm. So, Apple will cover the entire camera unit with sapphire glass. On the other hand, the lens will reduce the protrusion, which is more similar to the iPad Pro 2020. It has a thicker camera protrusion, but the lens design has fewer protrusions.

Mac Otakara believes that the iPhone 13 Pro will use sensor optical image stabilization, which makes it similar to the iPhone 12 Pro Max.
Speaking about the front of the iPhone 13, the website considers that the True Depth camera becomes shallower. The reason is that the top of the display (receiver) will be moved to the edge of the case. Therefore, new iPhones may have the same length but not the same thickness of bangs.
There are several other rumors about the upcoming iPhone 13. According to them, some models will use LTPO OLED display, support 120Hz refresh rate. Besides, it will support a faster A15 chip.