Also, virtualbox supports nested VMS "exclusively" on AMD chips.. in windows. Release notes indicate that it can also use Hyper-V as the hypervisor. Unsure if that's a potential workaround until MS resolves the issue but it's certainly worth a try.
Opened a ticket with MS and AMD. MS responded through our partner channel with a simple statement of "we're working on it". AMD has yet to respond but it definitely isn't their issue as it's supported on most every other hypervisor. This is silly.
Also, there's a competing thread at AMD's forums. I recommend bombarding them as well.
So, just plunked the cash down for a 2990wx and found out most of the drivers don't support server 2019, there's no nested virtualization, and MS still hasn't fixed the kernel scheduler bugs. This isn't a new platform anymore and it has been around for around two years. AMD's SVM is older than that. There is absolutely no excuse for this unless MS is intentionally driving business to Intel.