firmware: secure boot dbx with software-center but not apt?

[Steven Timorol <steven.timorol@disroot.org>]

Hello,

i get a message from 'gnome-software'
to update my firmware:
"
update configuration secure boot dbx:
Version 217:
This updates the dbx to the latest release from Microsoft which adds
insecure versions of grub and shim to the list of forbidden signatures
due to multiple discovered security updates.
"
but on the contrary
apt update/upgrade does not show anything to be updated

so what is this? 
and why doesn't apt show anything?
S.