IPhone X Size: 150.9 mm high, 75.7 mm wide, 8.3 mm thick, screen 6.1 inches. iPhone13 Size: 146.7 mm tall, 71.5 mm wide, 7.65 mm thick, 6.1-inch screen. It can be seen that in addition to the screen size of 6.1 inches, the other body size is completely different, although the difference is not large, but it is impossible to want a universal mobile phone case. So it's not universal.
No, the xr cannot be used in the shell with other apples. Because it is a full-screen launched in 2018, the phone is only equipped with a camera, while the previous iPhone X is 5.8 inch screen, it is 6.1 inch screen, and the later iPhone13 is also 6.1 inch screen, but it is equipped with three cameras, so their case is not universal, and the size of the button position has also changed a little. No way to generalize