direct_menu is no longer maintained, since it will be shipped integrated in Nextcloud 12
If you are running a version smaller than v0.10.2 when upgrading to Nextcloud 12 you will see the following error:
EXCEPTION
OC\IntegrityCheck\Exceptions\InvalidSignatureException
Certificate is not valid.
You can just disable and remove the direct_menu app to fix this.
Nextcloud/OwnCloud app to provide easy access to all apps in the header
sudo -u www-data php occ app:enable direct_menu