If you need to close the application access to the Internet, then on MIUI you can do this with the standard means of the system.
Why would you need it? For example, to prevent the app from updating, downloading ads, or sending analytics in the background.
Hold on the app icon and click "About App". Then click "Network connections" and uncheck all the boxes.
Please note that for system applications, you can only disable mobile internet. Wi-Fi access will work.