Created attachment 1622646 [details]
backtrace using gdb
Description of problem:
In f30, VirtualBox runs fine in wayland session but now broken in f31.
Steps to Reproduce:
1. GDK_BACKEND=X11 virtualbox
Qt WARNING: QSocketNotifier: Can only be used with threads started with QThread
(VirtualBox:9669): Gtk-WARNING **: 09:59:44.498: cannot open display: :0
This is a problem with VirtualBox, not gnome-shell. VirtualBox uses Qt, but has hard coded dependencies on X11 API, without forcing the Qt's backend to be the one it depends on.
A work aronud is: QT_QPA_PLATFORM=xcb virtualbox
VirtualBox is not a Fedora package, but an rpmfusion package. Seems to be a bug open about it already: https://bugzilla.rpmfusion.org/show_bug.cgi?id=5383
Marking as CANTFIX as it's not something gnome-shell can fix, and I cannot move it anywhere on this bug tracker.
(In reply to Jonas Ådahl from comment #1)
But why we don't have this problem on F30 and F29 ?
Because Qt defaults to the Wayland backend in F31, while in F29 and F30 it always used X11, meaning on always going via Xwayland.
*** Bug 1780888 has been marked as a duplicate of this bug. ***