Taking a screenshot on an Oppo A3s without using the power button is possible through alternative methods. One common method is using the three-finger swipe gesture: simply swipe down on the screen with three fingers to capture a screenshot. Another option is to utilize the Assistive Ball feature, if enabled. You can configure the Assistive Ball to include a screenshot function. By tapping the Assistive Ball, you can select the screenshot option without needing to press any physical buttons. These methods provide convenient alternatives for users who may have a malfunctioning power button or prefer a button-free screenshot experience on their Oppo A3s.