By default, the picture format is set to 4:3, but if we want to stream the photos/pictures to an HDTV and start a slide show, a 16:9 format is more sensible in order not to have black bars. Moreover, the Xiaomi devices offer a sufficiently large display in order to be able to shoot the photos better. Depending on the device, we have the following options:

Android 11 | MIUI 12.0
How to Change Camera frame (1:1/4:3/16:9) - Tap on  Camera
How to Change Camera frame (1:1/4:3/16:9) - Open the  Menu
How to Change Camera frame (1:1/4:3/16:9) - Set the  Camera frame
  1. Tap on Camera
  2. Open the Menu
  3. Set the Camera frame

Xiaomi Instructions