To take a screenshot on an Xiaomi Mi Mix 3 5G phone, you must press the Power key and the Volume down button at the same time.
For Xiaomi phones, you can call up a quick access menu that has a special icon to take a screenshot.
As a result, the screenshot will be placed in the gallery. After that, you can use the image to share it on social networks, instant messengers, or keep it as a photo.