qt: Screen reader is broken with composition on X11 and Windows

When running VLC 4.x with composition the screen reader no longer works.

This happens on:

  • Ubuntu --qt-compositor=x11 with Orca (Settings > Universal Access > Screen Reader).
  • Window --qt-compositor=dcomp with the narrator.

When testing with --qt-compositor=dummy it works fine on Ubuntu 20.04 and Windows 10.

Edited by Benjamin Arnaud