Sudoku does not launch from the application menu (Invalid desktop entry file)

Solution 1:

TL;DR

1. Check if gnome-sudoku is on your path by opening a terminal and just entering gnome-sudoku (under LXQT)
2. If that worked, please try to comment out DBusActivatable=true (or set it to false) in /usr/share/applications/org.gnome.Sudoku.desktop (or rather /usr/share/applications/gnome-sudoku.desktop in your case) and restart your LXQT session (logoff+logon). You must be su to edit (e.g. sudo nano ...). Launch Sudoku from the application menu.

Please tell me, if that worked.

Long version:

When looking up /usr/share/applications/org.gnome.Sudoku.desktop you will find the following line:

DBusActivatable=true

freedesktop.org writes in their specification:

A boolean value specifying if D-Bus activation is supported for this application. If this key is missing, the default value is false. If the value is true then implementations should ignore the Exec key and send a D-Bus message to launch the application. See D-Bus Activation for more information on how this works. Applications should still include Exec= lines in their desktop files for compatibility with implementations that do not understand the DBusActivatable key.

In short this means, Sudoku is not started by a plain command, but by sending a D-Bus message.

When deactivating the DBusActivatable entry, the Exec entry is used, which should work fine, though.

I strongly assume there must be an incompatibility between LXQT and Gnome regarding D-Bus and the gnome-games package.

I tested it without installing LXQT myself by starting dbus-monitor. With the switch set to true I can see the following message (Sudoku started via "Acitvate" method):

method call time=1636304012.356091 sender=:1.90 -> destination=org.gnome.Sudoku serial=7 path=/org/gnome/Sudoku; interface=org.freedesktop.Application; member=Activate
   array [
      dict entry(
         string "desktop-startup-id"
         variant             string "gtk-launch-24810-harald-desktop-gnome-sudoku-0_TIME0"
      )
   ]

With the switch commented out, this message does not appear, so the Exec command must be used directly.

As long as other Applications are running fine, I would not further invest time in figuring out what the exact reason for D-Bus mismatch between LXQT and Gnome is.

But if you have time, of course you can run dbus-monitor and maybe you find some explanation.