Great, that worked. 
At least, it booted, but I am stuck in a loop. I get the recovery key prompt and the system reboots soon after I enter it; rinse and repeat. 
But it’s progress, nonetheless.
Perhaps I should add that the VM is currently running with Secure Boot in setup mode, with an empty key database. But that should only matter for the TPM revealing the LUKS key. Entering the recovery key should eventually drop me to the desktop.