The tag is present in Lintian version 2.104.318. That is the most recent version we know about.
This .desktop file does not contain an "Icon" entry.
"Icon" is the name of the file (without the extension) of the icon displayed by this .desktop file. The icon is searched in the different icon themes. If the name is an absolute path, the given file will be used. The icon should be unique enough to help the user to recognise the application.
The desktop-file-validate tool in the desktop-file-utils package is useful for checking the syntax of desktop entries.
Please refer to https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s06.html, https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html, and Bug#854132 for details.