All reports of desktop-entry-contains-unknown-key for the archive. The extended description of this tag is:
The key on this line of the desktop entry is not one of the standard keys defined in the FreeDesktop specification, not one of the legacy KDE keywords, and one that does not begin with X-. It's most likely that the key was misspelled.
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/ar01s06.html for details.
This tag has not been emitted in any package tested by Lintian.