Package: linux-image-cloud-amd64 Severity: critical In stretch-backports the linux-image-cloud-amd64 package depends upon linux-image-4.19.0-0.bpo.2-cloud-amd64 however that package is not available
See https://packages.debian.org/stretch-backports/linux-image-cloud-amd64 There does seem to be an unsigned version at https://packages.debian.org/stretch-backports/linux-image-4.19.0-0.bpo.2-cloud-amd64-unsigned