Thanks for that solution. I had mentioned the issue recently in one of the Testing Updates threads, and was still waiting for a fix to be rolled out.
I made a couple of modifications to the text in the /usr/share/applications/org.kde.kioclient.desktop file though.
The first was changing kioclient5 to just kioclient, as kioclient5 is only a symbolic link to kioclient:
ls -laH /usr/bin | grep kioclient
-rwxr-xr-x 1 root root 64440 Dec 9 22:51 kioclient
lrwxrwxrwx 1 root root 9 Dec 9 22:51 kioclient5 -> kioclient
The second change was completely removing the X-Desktop-File-Install-Version=5.0 line. I don’t think it is required (although someone with more expertise than me may know more about this).
So this is what my /usr/share/applications/org.kde.kioclient.desktop file now looks like:
[Desktop Entry]
Name=KDE Kioclient (compat)
Exec=kioclient %u
Type=Application
NoDisplay=true
I just did a test run using a script I have which uses xdg-open to open multiple URLs in a browser. Everything worked as it should, and the irritating warning message is now gone.