Solution:
The first thing we must do to hide photos on Xiaomi mobiles is to go to the native gallery application, which is already installed with our mobile. When accessing it we will have to go to an album and select one or more images. Then you will see that a series of icons appear at the bottom of the screen.
To hide the content we will have to click on the Add album button and choose the Private album option. The first time we do it, we have to use an existing or new Mi account for the Xiaomi Cloud tool to start working on our mobile phone. Without this account, we will not be able to hide any element from the gallery, since it is a necessary and essential for this function.