Thank you for your support of Xiaomi products. The screen on the Xiaomi Pad 6S Pro appears too dark when placed in the tri-fold leather case due to the presence of magnets inside the case. These magnets can interfere with the Hall sensor, which is a component that detects the position of the tablet and helps manage screen functions. When the Hall sensor is affected by magnetic interference, it can cause the screen to go black or appear dim. To avoid this issue, ensure that no magnetic objects are placed near the tablet, and try removing the device from the case to see if the screen brightness improves.