Switch LibreOffice Backends: GTK3, GTK4, Qt5, Qt6

LibreOffice utilizes the Visual Class Library (VCL) plugin system on Linux to adapt its graphical interface to different desktop environments. By changing the SAL_USE_VCLPLUGIN environment variable, you can override the default UI rendering backend and switch between GTK3, GTK4, Qt5, and Qt6 (including KF5/KF6 for KDE Plasma). This guide provides the necessary steps to install the required backend packages, run LibreOffice with a specific backend temporarily via the terminal, set a permanent configuration, and verify the active rendering engine.

1. Install the Backend Packages

Before switching backends, ensure the corresponding VCL plugins are installed on your distribution.

• Ubuntu / Debian:

  sudo apt install libreoffice-gtk3 libreoffice-gtk4 libreoffice-qt5 libreoffice-qt6 libreoffice-kf5

• Fedora:

  sudo dnf install libreoffice-gtk3 libreoffice-gtk4 libreoffice-qt5 libreoffice-qt6 libreoffice-kf5

• Arch Linux:

  sudo pacman -S libreoffice-fresh

  (Arch packages include multiple VCL backends by default or as optional dependencies).

2. Identify the VCL Plugin Names

Set the SAL_USE_VCLPLUGIN environment variable to any of the following supported identifiers:

• gtk3: Modern GNOME / GTK3 interface.
• gtk4: Experimental GTK4 interface (availability depends on LibreOffice version).
• qt5: Generic Qt5 interface.
• qt6: Generic Qt6 interface.
• kf5: KDE Frameworks 5 integration with native file dialogs.
• kf6: KDE Frameworks 6 integration for modern Plasma 6 desktops.
• gen: Generic X11 interface (fallback mode with no toolkit theming).

3. Test Backends via Terminal

To launch LibreOffice with a specific backend temporarily, prepend the environment variable to the command:

• Launch with GTK3:

  SAL_USE_VCLPLUGIN=gtk3 libreoffice

• Launch with GTK4:

  SAL_USE_VCLPLUGIN=gtk4 libreoffice

• Launch with Qt5:

  SAL_USE_VCLPLUGIN=qt5 libreoffice

• Launch with Qt6:

  SAL_USE_VCLPLUGIN=qt6 libreoffice

• Launch with KDE Plasma (KF6):

  SAL_USE_VCLPLUGIN=kf6 libreoffice

4. Set the Backend Permanently

Method A: User Profile (Applies to all sessions)

Export the variable in your shell profile configuration (~/.profile, ~/.bashrc, or ~/.zshrc):

echo 'export SAL_USE_VCLPLUGIN=qt6' >> ~/.profile

Log out and log back in to apply the changes.

Method B: Desktop Launcher (Applies only to app menu launches)

1. Copy the system desktop entry to your local application directory:

   cp /usr/share/applications/libreoffice-writer.desktop ~/.local/share/applications/

2. Open ~/.local/share/applications/libreoffice-writer.desktop in a text editor.

3. Modify the Exec line to define the variable:

   Exec=env SAL_USE_VCLPLUGIN=gtk3 libreoffice --writer %U

5. Verify the Active Backend

To confirm that LibreOffice is using the desired UI backend:

1. Open LibreOffice.
2. Navigate to Help > About LibreOffice.
3. Locate the User Interface entry in the information box. It will display the active backend (e.g., UI render: default; VCL: gtk3 or VCL: qt6).