I've used virtmanager to create a virtual machine. The installation media is the Debian netinstaller (Version 10, buster). The installation works without problems. Restart failed: no boot device was found. Starting the recovery mode from the uninstaller image: All resources are available, the chroot instance is working properly.
# I used the recovery mode to reinstall grub: grub-install /dev/sda update-grub
I was waiting to see the grub dialog box during startup. I found the message "no boot device found"