What if the clock doesn't change after Xiaomi's mobile phone changes its theme?

First, make sure that the theme you change contains a clock. If it is a free desktop clock such as Angry Birds, you need to change the mobile phone system to a development version. If you want to change the desktop clock, press and hold the gap between the scrolling desktop and the stationary icon to delete the original clock, and you can add it yourself.

That is, after you enter the editing mode (you should know this), delete the 2*2 clock, pull the option at the bottom to the right, select the analog clock and drag it up, and it will automatically become the matching clock for your current theme.