Many eons ago I got a working VM of OS X 10.6 server working on earlier versions of VMWare Fusion, back in the v8 and earlier era. I recently tried reviving this old VM on a newly installed copy of VMWare Fusion 12.1.1, and it simply fails out with a "Failed to power on [name of VM file]" error. Is there some stupidly obvious solution to this that I'm missing, perhaps some conversion utility for really old earlier VMs?
Is your new Fusion instance on a Mac with an Intel processor or the Apple M1 processor?
It’s a newish M1 MacBook Air.
That's the problem then, Fusion cannot power on any VM on the M1 today.
In the future it will, but not x86-based OSes.