I was testing out automatic disk decryption with the TPM and secure boot in a Qemu/KVM VM. I had Arch set up with a UKI, I followed this process to enable secure boot and enroll the keys which all worked fine. I then used systemd-cryptenroll to unlock the drive automatically which again worked great.

This is the part where I then messed up and I'm not quite sure how or why. I wanted to check that disabling secure boot prevented unlocking of the drive, so I enabled the boot menu in the VM settings, entered it and reset the secure boot settings. As expected I then needed to enter the password again. I then wanted to re-enable it so I re-ran sbctl enroll-keys -m to re-enroll the keys, and rebooted as my UKI was already signed. And that was that, VM completely dead. No matter whether I try to boot from the virtual disk, the virtual CD drive, or even the virtual network adapter all I get is a black screen with "Display output is not active". I can't even enter the firmware menu again because I no longer get that prompt.

It doesn't matter that this happened and I don't need to fix it because it was just a throwaway VM which I've now deleted, but I would like to know what caused it so I can avoid potentially bricking real hardware in the future