FWIW 7.0.14-8-pve works and boots just fine for me. Asrock WRX80 Creator R2.0 and 4x1TB Corsair MP600 Pro LPX NVME on an Asus Hyper M.2 Gen4 card (x4x4x4x4, passive card)
E: also works with the latest 7.0.14-11-pve
E2: I am using systemd-boot...
The nested VM in the title is quite misleading or not part of the problem here.
The main problem is that 9.2 PVE installer ISO does not boot on Hyper-V (at least Gen2) at all, 9.1 works fine.
Lots of hv_ modules missing?
Edit: same thing...