All good thoughts.

But it turns out the problem was more catastrophic than I had imagined.

A few months ago my MBP crashed and would not power on, so it was shipped back to Apple for repair. They fixed it and, as they warned, wiped the SSDs clean when they reinstalled the OS.

I hadn't used the VMs since then, until attempting the Big Sur + Fusion 12 Pro upgrade.

I restored the drives from Backblaze, figuring I'd be good since the VM folder wasn't excluded.

Bad assumption. Backblaze excludes vmx and vmdk files by default, and I didn't introduce Time Machine backups until after the Backblaze restoration.

So it looks like my VMs are gone forever and will have to be rebuilt.

Thanks anyway for the quick assist!