My testing results with the grub4dos-0.4.6a_for_UEFI-2020-11-26:
I created a fixed size 2.3 GB VHD (unformated) on a partition of my internal HD, initialized it as MBR, then formated as Win 6.x MBR, first partition is 128 MB FAT-32 0C Active, and second is NTFS (the rest of the espace), by means of wimlib-clc I installed (on Compact LZX mode) the Mini-10-x64 on NTFS partition and created manually the Boot Files/folders on the FAT-32 partition, and edited both BCDs with BootIce, See attached pictures), latter made a new Ramboot entry on old menu.lst (for grub4dos for MBR) as usuall for the VHD located on internal HD:
title 10x64-UEFI.vhd - SVBus RAMDISK - 2.3 GB - map as (hd) for MBR boot
find --set-root --ignore-floppies /10x64-UEFI.vhd
map --top --mem /10x64-UEFI.vhd (hd)
It booted very fine, not a single issue, so this confirms a VHD with 2 partitions (having boot files/folders on FAT-32 partition) is capable to Ramboot very fine (at least when MBR booting).
So far I have being able to UEFI boot Win10XPE_x64.ISO from internal HD or USB, this is my very simple menu.lst (good to start testing with the minimum features):
title Start Win10XPE_x64.ISO - UEFI boot
find --set-root /images/Win10XPE_x64.ISO
map /images/Win10XPE_x64.ISO (0xff)
title 10x64-UEFI.vhd SVBus RAMDISK - UEFI boot
find --set-root /10x64-UEFI.vhd
map --mem /10x64-UEFI.vhd (hd)
title start Grub2 menu
find --set-root /EFI/Boot/BOOTX64.EFI
title command line
title Exit grub4dos
NOTE-1: CSM and Secure Boot are disabled, menu.lst is located on: \EFI\grub\menu.lst; \images\Win10XPE_x64.ISO is on FAT-32 partition; 10x64-UEFI.vhd is on the root of a NTFS partition, BOOTX64.EFI from grub4dos for UEFI was renamed to g4ex64.efi and copied to: \EFI\Boot\g4ex64.efi and an alternative UEFI boot option pointing to it was created on UEFI using BootIce, used when booting from internal HD, not required when booting from USB
Win10XPE_x64.ISO boots very fine with no issues from USB or internal HD
10x64-UEFI.vhd is not found on USB or internal HD, even if using (hd0,1), (hd1,1) or (hd2,1)/10x64-UEFI.vhd, it looks like the NTFS partitions can't be accessed/readen by grub4dos for UEFI.
NOTE-2: This were all MBR partitions, but also tested making a GPT partitioned USB device and botting from it got same results, 10x64-UEFI.vhd is not found on the GPT NTFS of this USB.
Also noticed the entry:
Makes the PC reboot not shutdown