When running update-desktop-database, I'm getting this error:

michel@debian:~$ sudo update-desktop-database
Error in file "/usr/share/applications/org.gnome.font-viewer.desktop":
"font/ttf" is an invalid MIME type ("font" is an unregistered media type)
Error in file "/usr/share/applications/org.gnome.font-viewer.desktop":
"font/otf" is an invalid MIME type ("font" is an unregistered media type)

I had to fix the issue manually by removing the invalid MIME types. That's why
debsums reported that this file has been changed.

Bug #910820 notes that update-desktop-database complained about "font/ttf"
in gnome-font-viewer.desktop.  The "font" top-level media type was
registered by RFC 8081 in February 2017, so in October 2018 the failure to
accept it was a bug in desktop-file-utils.  Anyway, it was fixed by
version 0.24 of desktop-file-utils in 2019, which added support for the
"font" top-level media type.