application failed to start because no Qt platform plugin could be initialized

Since I have updated to 1.1.82.200, the application no longer launches. Instead, it closes with the following error:

```
(base) duxon@penguin:~$ flatpak run com.valvesoftware.SteamLink
qt.qpa.xcb: could not connect to display
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.
```

This happens on a Debian (buster) on Crostini where I had no issues before. Any ideas why that happens?

Start by reproducing the failure with `flatpak run com.valvesoftware.SteamLink` on Debian Buster under Crostini and inspect the Qt platform-plugin and display errors. Done means identifying the launch-environment or packaging change that caused the regression and confirming that Steam Link starts normally without the xcb initialization error.

Written by the indexing model from the issue text.