The tag is present in Lintian version 2.104.244. That is the most recent version we know about.
The key on this line of the desktop entry has been deprecated in the FreeDesktop specification. If the key is "KDE Desktop Entry", the right fix is normally changing it to "Desktop Entry".
The desktop-file-validate tool in the desktop-file-utils package is useful for checking the syntax of desktop entries.
Refer to https://specifications.freedesktop.org/desktop-entry-spec/latest/apc.html for details.