Installing MTZ themes on Xiaomi MIUI 12: A complete guide to error solutions

Installing custom themes in MTZ format on Xiaomi smartphones with a shell MIUI 12 is a process that opens up access to unique interface designs that are not available in the official theme store. Although MIUI offers hundreds of off-the-shelf solutions, many users prefer to install third-party themes created by enthusiasts. However, there are difficulties, from the lack of built-in support for MTZ- files to application errors.

In this article, we will discuss three official installation methods (via built-in theme store, manual download, and third-party apps), and we will also look at workarounds for cases where the system blocks the boot, paying special attention to common errors – for example, when the theme is installed but not applied, or when the device gives a message of incompatibility. If you are using the Xiaomi Redmi Note 9 Pro, Mi 10 or another model on MIUI 12, this guide will help avoid typical problems.

What is it? MTZ-Themes and Why They Are Better Than Standard

MTZ (Mi Theme Zip) is an archive with design files for MIUI, which includes:

• 🎨 Application icons (in PNG or SVG format)
• 📱 Background images for desktop and lock
• 🔧 Styles of interface elements (buttons, menus, notifications)
• 🎵 Sound circuits (optional if supported by the theme)

Advantages of MTZ-themes over standard:

• ✅ Unique: Many themes are created by enthusiastic designers and do not duplicate official solutions.
• ✅ Flexibility: You can customize a particular smartphone model (e.g., for POCO X3 NFC with a Full HD+ display).
• ✅ Ad-free: Unlike some of the themes from the official store, custom versions are often devoid of intrusive banners.

There are, however, downsides:

• ⚠️ Risk of incompatibility: Themes created for MIUI 11 may not be displayed correctly in MIUI 12.
• ⚠️ Security: Files from unverified sources may contain malicious code.

Preparation of the smartphone: what to do before installation

Before installing MTZ-Tem, you need to follow several steps to avoid errors:

1. Check the MIUI version: go to Settings → About Phone → MIUI version. Make sure you have MIUI 12 installed (or newer). Older versions (such as MIUI 11) may require other methods.
2. Update the Themes app: Open Google Play → My apps → Themes and install the latest updates.
3. Enable installation from unknown sources: Go to Settings → Applications → Application Management → Themes. Activate Installation from unknown sources.

Make a backup copy.

Topics → My Topics → Save

If you plan to install themes through ADB or third-party launchers, additionally:

• 🔧 Enable Developer Mode (7 times click on MIUI in the settings).
• 🔧 Activate Debugging on USB In Settings → Additionally. → For developers.

⚠️ Warning: Some devices (e.g., Redmi 9A with MIUI 12.0.3) may display a security risk alert after debugging USB, and you can only ignore it if you download the theme from a trusted source.

Method 1: Install MTZ through the official application "Themes"

The easiest method is to download the MTZ- file through a standard application, but it does not always work, since MIUI 12 limits the installation of third-party themes.

Step-by-step:

1. Download the MTZ- file to your device (for example, via a browser or Telegram).
2. Open the Topic app.
3. Go to the section My topics → Local.
4. Click on the Import button (or + in the upper right corner).
5. Select the downloaded.mtz file and confirm the installation.

If the Import button is not available:

• 🔄 Try renaming the file to.zip and then back to.mtz.
• 📂 Move the file to the MIUI/theme folder on the internal drive.
• 🔄 Restart the device and try again.

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If the theme doesn’t apply after installation, try applying a standard theme first (e.g., “Default”) and then selecting a custom theme again.

Method 2: Manual installation via file manager

If the standard method didn't work, you can try manual installation through the file manager, which is suitable for devices where the Themes app blocks imports.

Algorithm of action:

1. Download the MTZ- file and rename it to.zip (e.g., theme.mtz → theme.zip).
2. Unclose the file to any folder on the device.
3. Copy the archive contents into a folder: /sdcard/MIUI/theme/[NAZVANIE_TEMY] (where [NAZVANIE_TEMY] is the name of the theme folder, for example, DarkNebula).
4. Reset the device.
5. Open the Themes → Local app and select the set theme.

If the MIUI/theme folder does not exist:

• 📁 Create it manually through a file manager (e.g., Mi File Explorer or Solid Explorer).
• 🔧 Make sure that the Themes app has storage access rights (Settings → Apps → Rights → Warehouse).

⚠️ Warning: On some firmware (e.g., MIUI 12.5 Enhanced), the /sdcard/MIUI/theme folder may be hidden. To see it, turn on the hidden files in the file manager settings.

Method 3: Use of third-party applications (Theme Manager, MTZ Installer)

If the first two methods don't work, third-party utilities will come to the rescue.

• 📱 MTZ Installer (requires root rights on some devices)
• 🎨 Theme Manager for MIUI (works without root, but may request additional permissions)
• 🔧 MiXplorer (file manager with MTZ support)

Instructions for Theme Manager:

1. Install the application from 4PDA or XDA Developers.
2. Open Theme Manager and provide all the permissions you have requested.
3. Press Import MTZ and select the downloaded file.
4. Confirm the installation and restart the device.

Advantages of this method:

• ✅ Works on most Xiaomi devices, including the POCO and Black Shark.
• ✅ Supports batch installation of multiple themes.
• ✅ Allows you to edit topics before use.

Disadvantages:

• ⚠️ Some applications (e.g., MTZ Installer) require root rights to work properly.
• ⚠️ Risk of blocking a Mi Account when using modified themes (rarely, but it does happen).

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The application side is the most reliable way to install the MTZ- theme if standard methods do not work, but check the feedback on the program on the forums before using it (4PDA, XDA).

Solving Common Errors When Installing MTZ

Even with the right installation, users often face problems. Consider top-5 errors and their solutions:

1. Error: "Theme is not supported by your version of MIUI" Reason: Theme is created for another version of the shell (for example, for MIUI 13). Solution: Find a version of the theme specifically for MIUI 12 or edit the description.ini file inside the archive (knowledge required).
2. Error: "Failure to apply the theme" Reason: Conflict with current settings or damaged cache Solution: Clear the cache of the "Themes" application (Settings → Applications → Topics → Storage → Clear cache).
3. Error: "File corrupted" Reason: Incomplete download or incorrect extension. Solution: Upload the file and check that the extension is.mtz (sometimes browsers save it as.zip).
4. Error: Theme applies but icons are knocked down Reason: Icon resolutions mismatch in the theme and your launcher Solution: Install a Nova Launcher or POCO Launcher launcher and apply the theme through it.
5. Error: After the reboot, the theme resets Reason: System reset or conflict with energy saving mode. Solution: Turn off battery optimization for the Themes app (Settings → Battery → Battery Optimization → Themes → No Limits).

Critical information: On some devices (e.g. Xiaomi Mi 11 Ultra with MIUI 12.5) after installing MTZ-Temes, the Always-on Display functionality may disappear. To return it, apply the standard theme, and then re-activate AOD in the settings.

Where to download MTZ-themes for MIUI 12: verified sources

Not all sites and channels offer safe and workable themes, but here is a list of proven sources:

Safety recommendations:

• 🛡️ Before installing, check files via VirusTotal or Dr.Web.
• 🔍 Read the comments below the topic – if there are bug complaints, it’s better to look for another option.
• 📥 Only download from high-rated (4.5+ stars) topics.

⚠️ Warning: Avoid sites that ask to disable antivirus before downloading or offer "hacked" versions of themes.This could result in data theft or device locking through Mi Cloud.

FAQ: Frequent questions about installing MTZ-Tem on MIUI 12