Telegram Desktop failing to start with a qt.qpa.xcb error on Linux is usually caused by missing libraries, faulty environment variables (e.g., QT_QPA_PLATFORM), or X11/Wayland authorization issues. Fixes include installing libxcb-cursor0, removing conflicting QT_QPA_PLATFORM variables, or using xhost +local:root for Snap/Flatpak versions. 

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Here are the specific solutions:

Install Missing Libraries (Debian/Ubuntu): The error often stems from a missing libxcb-cursor0 package. Run:

bash
sudo apt update
sudo apt install libxcb-cursor0 

Fix Environmental Variable Conflict: If you set QT_QPA_PLATFORM to gtk or wayland, it may cause issues with the default XCB backend. Remove it by editing ~/.bashrc or running:

bash
unset QT_QPA_PLATFORM telegram-desktop 

Fix Snap/Flatpak Permissions: If running via Snap, the app may not have permission to access the display. Fix this by running:

bash
xhost +local:root
snap run telegram-desktop

