Your phone may not support knuckle gestures, the operation was performed incorrectly, or certain system files have been deleted by mistake. To resolve the issue, perform the following:

EMUI 9.1 and Magic UI 2.1 or later: Open Settings and search for Knuckle screenshots/Record screen. If no results are found, it means that your phone does not support knuckle gestures.

• Do not use magnetic attachment or metal protective cases, which may affect hand gesture recognition, causing knuckle screenshots or screen recording failures.
• To take a screenshot, knock twice with one knuckle. To record the screen, knock twice with two knuckles and make sure that they touch the screen at the same time.
• Knock on the screen in the same way as you would knock on a door.
• Make sure to knock twice quickly (with the interval not exceeding 0.25 seconds).
• If your phone is using a leather case, knock on the screen with one hand while holding your phone firmly with the other hand.
• Avoid taking a second screenshot immediately after the first screenshot, as the image requires time to process. Wait approximately 2 seconds after the thumbnail of the previous screenshot disappears.
• When taking a partial screenshot, knock on the screen with a knuckle and hold until a blue dot appears, draw an enclosed area, and make sure the two ends of the blue line meet. Be sure to apply a sufficient amount of force when knocking your knuckle against the screen, similar to knocking on a door.