How to remove ads from a Xiaomi MUI mobile phone

Note: This is applicable and updated for MUI versions up to March 2021.

Remove ads by disabling the MSA process

Open the Settings app.
Navigate to Passwords & security > Authorisation & revocation.
You'll see 'msa' listed here, with a little green Android logo. Toggle this setting off.
While you're here, do the same for GetApps too, which should be the last one in the list
.
You'll get a 10-second warning message, asking you if you're sure you want to do it.
After the countdown, press Revoke.
Even if you reboot your phone, MSA should still be disabled.

In the Passwords & security sub-menu, go to Privacy and scroll down to the User Experience Programme section.
Here you should disable the toggle switch for User Experience Programme and Send diagnostic data automatically.
Below that, you'll see Ad services. Here, disable Personalised ad recommendations.

To disable ads from Mi Video:

Open the Mi Video app.
Tap the Profile tab at the bottom right corner and tap Settings.
Disable Online recommendations, Push notifications and Personalised recommendations.

To disable ads from Mi Music:

Open the Music app.
Tap the hamburger menu (three horizontal lines) in the top, left corner.
Tap Settings > Advanced settings and scroll all the way down and disable Receive recommendations. You could disable the other settings below it too.

To disable ads from File Manager:

Open the File Manager app.
Tap the hamburger icon in the top, left corner.
Tap Settings > About.
Here, disable Recommendations.

To disable ads from Downloads:

Open the Downloads app (in the Tools folder).
Tap the three vertical dots in the top right corner of the app.
Disable Show recommended content.

To disable ads from Mi Browser:

Open the Browser app.
Tap the hamburger menu in the upper, right corner and tap the settings icon (shaped like a cog).
Disable Content feed (if you don't want weird content randomly popping up).
Go to Advanced and make sure Show ads toggle is disabled.
Go back a step to the main Settings page of the app and then tap on Privacy & security.
Here, make sure Personalised services is disabled.

To disable ads from Mi Security:

Open the Security app.
Tap the cog icon in the upper right corner of the app.
In the Feature Settings section, tap Cleaner and disable Receive recommendations down the list.
You can also disable the Remind to clean option.
Go back a step and in the main Settings menu of the app, scroll down and disable Receive recommendations.
For more privacy, you could go to Data Usage option and disable Report data usage info toggle.

To disable ads from Themes:

Open the Themes app.
Tap the My page tab, in the bottom right corner.
Tap Settings and disable Recommendations.

Disabling Promoted apps

Some default folders such as Games and More apps tend to show you 'Promoted apps' when you open them.

To get rid of this, simply open such a folder and long-press the name, in order to rename it. This will give you a toggle switch below to turn off 'Promoted apps.'

Removing Promoted Apps from MIUI folders

You have to go to each folder where the promoted apps are showing. Open the folder and tap on the name. Right below the name will appear a “Promoted Apps” slider (as seen in the screenshot below). Toggle the slider to disable promoted apps and that’s it.