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 10 (MIUI 12.0)
Step 1:  Open the  Camera app
Step 2:  Open the  menu
Step 3:  Choose  1:1 / 3:4 / 9:16 / Full
  1. Open the Camera app
  2. Open the menu
  3. Choose 1:1 / 3:4 / 9:16 / Full

Xiaomi Instructions