I requires shim-unsigned instead of shim-signed. Currently I have on my system
15.8 for helpers, 15.8 for shim-unsigned but still 15.7 for signed.
dpkg -l shim*
Souhait=inconnU/Installé/suppRimé/Purgé/H=à garder
| État=Non/Installé/fichier-Config/dépaqUeté/échec-conFig/H=semi-installé/W=attend-traitement-déclenchements
|/ Err?=(aucune)/besoin Réinstallation (État,Err: majuscule=mauvais)
||/ Nom Version Architecture Description
+++-=========================-============-============-=====================================================>
un shim <aucune> <aucune> (aucune description n'est disponible)
ii shim-helpers-amd64-signed 1+15.8+1 amd64 boot loader to chain-load signed boot loaders (signed>
ii shim-signed:amd64 1.40+15.7-1 amd64 Secure Boot chain-loading bootloader (Microsoft-signe>
ii shim-signed-common 1.40+15.7-1 all Secure Boot chain-loading bootloader (common helper s>
ii shim-unsigned:amd64 15.8-1 amd64 boot loader to chain-load signed boot loaders under S>