I did some research on this issue.
1. Desktop file is created by a script "add-calamares-desktop-icon" which
is launched by /etc/xdg/autostart/calamares-desktop-icon.desktop
Both files belong to the package calamares-settings-debian
2. "X-GNOME-Autostart-Phase" on calamares-desktop-icon.desktop b
I can confirm that this issue is still present in the latest
debian-live-12.6.0-amd64-kde.iso
I've also checked other official Live ISOs.
GNOME, LXDE, LXQT, MATE, XFCE have install-debian.desktop files at
$HOME/Desktop.
For some reason, it's missing there on the KDE Live edition.
"Install Debian"
